U.S. patent application number 17/183997 was filed with the patent office on 2021-12-16 for control policy settings for electrical stimulation therapy.
The applicant listed for this patent is Medtronic, Inc.. Invention is credited to Hank Bink, Duane L. Bourget, Kristin N. Hageman, Jiashu Li, Laura Ann Skarie.
Application Number | 20210387002 17/183997 |
Document ID | / |
Family ID | 1000005511264 |
Filed Date | 2021-12-16 |
United States Patent
Application |
20210387002 |
Kind Code |
A1 |
Bourget; Duane L. ; et
al. |
December 16, 2021 |
CONTROL POLICY SETTINGS FOR ELECTRICAL STIMULATION THERAPY
Abstract
This disclosure is directed to devices, systems, and techniques
for controlling electrical stimulation. In some examples, a system
includes a user interface and processing circuitry. The processing
circuitry is configured to output, for display by the user
interface, a message requesting the patient perform a set of
actions, receive, from the user interface, user input indicative of
a patient response associated with the set of actions, and
determine, based on the user input, one or more adjustments to a
control policy which controls electrical stimulation delivered by a
medical device based on a plurality of evoked compound action
potentials (ECAPs) sensed by the medical device.
Inventors: |
Bourget; Duane L.; (Andover,
MN) ; Hageman; Kristin N.; (Dayton, MN) ;
Bink; Hank; (Golden Valley, MN) ; Li; Jiashu;
(Mounds View, MN) ; Skarie; Laura Ann;
(Minnetonka, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Medtronic, Inc. |
Minneapolis |
MN |
US |
|
|
Family ID: |
1000005511264 |
Appl. No.: |
17/183997 |
Filed: |
February 24, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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63037361 |
Jun 10, 2020 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/36062 20170801;
A61N 1/37247 20130101; A61N 1/36132 20130101; A61N 1/37241
20130101 |
International
Class: |
A61N 1/36 20060101
A61N001/36; A61N 1/372 20060101 A61N001/372 |
Claims
1. A system comprising: a user interface; and processing circuitry
configured to: output, for display by the user interface, a message
requesting the patient perform a set of actions; receive, from the
user interface, user input indicative of a patient response
associated with the set of actions; and determine, based on the
user input, one or more adjustments to a control policy which
controls electrical stimulation delivered by a medical device based
on at least one evoked compound action potentials (ECAP) sensed by
the medical device.
2. The system of claim 1, wherein the system further comprises:
communication circuitry configured to communicate with the medical
device, wherein the processing circuitry is configured to output,
to the medical device via the communication circuitry, an
instruction to configure the one or more adjustments to the control
policy.
3. The system of claim 1, wherein the electrical stimulation
comprises a plurality of informed pulses and a plurality of control
pulses, each control pulse of the plurality of control pulses
eliciting a respective ECAP of the plurality of ECAPs, wherein the
control policy controls, based on the plurality of ECAPs, one or
more parameters corresponding to the plurality of control pulses
delivered by the medical device, and wherein the control policy
controls, based on the plurality of ECAPs, one or more parameters
corresponding to the plurality of informed pulses delivered by the
medical device.
4. The system of claim 1, wherein the control policy controls one
or more parameters of the electrical stimulation therapy delivered
by the medical device, wherein the electrical stimulation therapy
comprises a plurality of stimulation pulses, and wherein to
determine the one or more adjustments to the control policy, the
processing circuitry is configured to: determine the one or more
adjustments in order to cause the control policy to perform any one
or combination of decrease a decrement step size or a decrement
step rate of the plurality of stimulation pulses responsive to one
or more events associated with the patient response, increase the
decrement step size or the decrement step rate of the plurality of
stimulation pulses responsive to the one or more events associated
with the patient response, decrease an increment step size or an
increment step rate of the plurality of stimulation pulses
responsive to the one or more events associated with the patient
response, and increase the increment step size or the increment
step rate of the plurality of stimulation pulses responsive to the
transient one or more events associated with the patient
response.
5. The system of claim 1, wherein the processing circuitry is
further configured to: output, for display by the user interface, a
set of requests, wherein each request of the set of requests
comprises a prompt for information relating to one or more patient
sensations corresponding to the action, and wherein to receive the
user input indicative of the patient response, the processing
circuitry is configured to: receive, from the user interface, a set
of responses, wherein each response of the set of responses
represents a patient response to a respective request of the set of
requests.
6. The system of claim 5, wherein the processing circuitry is
configured to: output, for display by the user interface, a first
request of the set of requests, wherein the first request includes
a prompt for the user to indicate whether the set of actions caused
an undesirable sensation during the set of actions; and receive,
from the user interface, a first response of the set of responses,
wherein the first response comprises a patient response that the
set of actions caused an undesirable sensation during the set of
actions or a patient response that the set of actions did not cause
an undesirable sensation during the set of actions.
7. The system of claim 6, wherein responsive to receiving the
patient response that the set of actions lead to one or more
undesirable sensations during the set of actions, the processing
circuitry is configured to: output, for display by the user
interface, a group of second requests of the set of requests,
wherein the group of second requests include a prompt for the user
to identify the undesirable sensation from a menu of possible
undesirable sensations; receive, from the user interface, a group
of second responses of the set of responses, wherein the group of
second responses comprise a user identification of the undesirable
sensation from the menu of undesirable sensations; and determine,
based on the group of second responses, the one or more adjustments
to the control policy.
8. The system of claim 6, wherein responsive to receiving the
patient response that the set of actions did not cause an
undesirable sensation during the set of actions, the processing
circuitry is configured to: output, for display by the user
interface, a second request of the set of requests, wherein the
second request includes a prompt for the user to indicate whether
the set of actions caused an undesirable sensation after the set of
actions; and receive, from the user interface, a second response of
the set of responses, wherein the second response comprises a
patient response that the set of actions caused an undesirable
sensation after the set of actions or a patient response that the
set of actions did not cause an undesirable sensation after the set
of actions.
9. The system of claim 8, wherein responsive to receiving the
patient response that the set of actions caused an undesirable
sensation after the set of actions, the processing circuitry is
configured to: output, for display by the user interface, a group
of third requests of the set of requests, wherein the group of
third requests include a prompt for the user to identify the
undesirable sensation from a menu of possible undesirable
sensations; receive, from the user interface, a group of third
responses of the set of responses, wherein the group of third
responses comprise a user identification of the undesirable
sensation from the menu of undesirable sensations; and determine,
based on the group of third responses, the one or more adjustments
to the control policy.
10. The system of claim 9, wherein the set of actions is a first
set of actions, wherein the message is a first message, and wherein
responsive to receiving the patient response that the first set of
actions did not cause an undesirable sensation after the first set
of actions, the processing circuitry is configured to: determine
whether to prompt the patient to perform a second set of actions;
and responsive to determining to prompt the patient to perform a
second set of actions, output a second message for display by the
user interface, the second message requesting the patient to
perform the second set of actions.
11. The system of claim 1, wherein the processing circuitry is
further configured to: output, prior to outputting the message
requesting the patient to perform the set of actions, an
instruction for the medical device to measure one or more
parameters; and receive, from the medical device, data indicative
of the one or more measured parameters, wherein the data
corresponds to a period of time including the set of actions
performed by the patient.
12. The system of claim 11, wherein the one or more parameters
include any one or combination of a stimulation amplitude of one or
more stimulation pulses of the electrical stimulation therapy,
characteristics of evoked compound action potentials (ECAPs)
responsive to the one or more stimulation pulses, an electrogram
(EGM) of the patient, a motion level of the patient, or any
combination thereof.
13. The system of claim 1, wherein the medical device comprises an
implantable medical device (IMD).
14. The system of claim 1 wherein an external device comprises the
user interface.
15. A method comprising: outputting, by processing circuitry for
display by the user interface, a message requesting the patient
perform a set of actions; receiving, by the processing circuitry
from the user interface, user input indicative of a patient
response associated with the set of actions; and determining, by
the processing circuitry based on the user input, one or more
adjustments to a control policy which controls electrical
stimulation delivered by a medical device based on at least one
evoked compound action potentials (ECAP) sensed by the medical
device.
16. The method of claim 15, further comprising outputting, by the
processing circuitry to the medical device via communication
circuitry, an instruction to configure the one or more adjustments
to the control policy.
17. The method of claim 15, wherein the control policy controls one
or more parameters of the electrical stimulation therapy delivered
by the medical device, wherein the electrical stimulation therapy
comprises a plurality of stimulation pulses, and wherein to
determining the one or more adjustments to the control policy
comprises: determining the one or more adjustments in order to
cause the control policy to perform any one or combination of
decrease a decrement step size or a decrement step rate of the
plurality of stimulation pulses responsive to one or more events
associated with the patient response, increase the decrement step
size or the decrement step rate of the plurality of stimulation
pulses responsive to the one or more events associated with the
patient response, decrease an increment step size or an increment
step rate of the plurality of stimulation pulses responsive to the
one or more events associated with the patient response, and
increase the increment step size or the increment step rate of the
plurality of stimulation pulses responsive to the transient one or
more events associated with the patient response.
18. The method of claim 15, wherein the method further comprises:
outputting, by processing circuitry for display by the user
interface, a set of requests, wherein each request of the set of
requests comprises a prompt for information relating to one or more
patient sensations corresponding to the action, and wherein to
receiving the user input indicative of the patient response
comprises: receiving, from the user interface, a set of responses,
wherein each response of the set of responses represents a patient
response to a respective request of the set of requests.
19. The method of claim 18, wherein the method further comprises:
outputting, by processing circuitry for display by the user
interface, a first request of the set of requests, wherein the
first request includes a prompt for the user to indicate whether
the set of actions caused an undesirable sensation during the set
of actions; and receiving, by processing circuitry from the user
interface, a first response of the set of responses, wherein the
first response comprises a patient response that the set of actions
caused an undesirable sensation during the set of actions or a
patient response that the set of actions did not cause an
undesirable sensation during the set of actions.
20. The method of claim 19, wherein responsive to receiving the
patient response that the set of actions lead to one or more
undesirable sensations during the set of actions, the method
further comprises: outputting, by the processing circuitry for
display by the user interface, a group of second requests of the
set of requests, wherein the group of second requests include a
prompt for the user to identify the undesirable sensation from a
menu of possible undesirable sensations; receiving, by the
processing circuitry from the user interface, a group of second
responses of the set of responses, wherein the group of second
responses comprise a user identification of the undesirable
sensation from the menu of undesirable sensations; and determining,
by the processing circuitry based on the group of second responses,
the one or more adjustments to the control policy.
21. The method of claim 19, wherein responsive to receiving the
patient response that the set of actions did not cause an
undesirable sensation during the set of actions, the method further
comprises: outputting, by the processing circuitry for display by
the user interface, a second request of the set of requests,
wherein the second request includes a prompt for the user to
indicate whether the set of actions caused an undesirable sensation
after the set of actions; and receiving, by the processing
circuitry from the user interface, a second response of the set of
responses, wherein the second response comprises a patient response
that the set of actions caused an undesirable sensation after the
set of actions or a patient response that the set of actions did
not cause an undesirable sensation after the set of actions.
22. The method of claim 21, wherein responsive to receiving the
patient response that the set of actions caused an undesirable
sensation after the set of actions, the method further comprises:
outputting, by the processing circuitry for display by the user
interface, a group of third requests of the set of requests,
wherein the group of third requests include a prompt for the user
to identify the undesirable sensation from a menu of possible
undesirable sensations; receiving, by the processing circuitry from
the user interface, a group of third responses of the set of
responses, wherein the group of third responses comprise a user
identification of the undesirable sensation from the menu of
undesirable sensations; and determining, by the processing
circuitry based on the group of third responses, the one or more
adjustments to the control policy.
23. The method of claim 22, wherein the set of actions is a first
set of actions, wherein the message is a first message, and wherein
responsive to receiving the patient response that the first set of
actions did not cause an undesirable sensation after the first set
of actions, the method further comprises: determining, by the
processing circuitry, whether to prompt the patient to perform a
second set of actions; and responsive to determining to prompt the
patient to perform a second set of actions, outputting, by the
processing circuitry, a second message for display by the user
interface, the second message requesting the patient to perform the
second set of actions.
24. The method of claim 15, further comprising: outputting, by the
processing circuitry prior to outputting the message requesting the
patient to perform the set of actions, an instruction for the
medical device to measure one or more parameters; and receiving, by
the processing circuitry from the medical device, data indicative
of the one or more measured parameters, wherein the data
corresponds to a period of time including the set of actions
performed by the patient.
25. A computer-readable medium comprising instructions that, when
executed by a processor, causes the processor to: output, for
display by the user interface, a message requesting the patient
perform a set of actions; receive, from the user interface, user
input indicative of a patient response associated with the set of
actions; and determine, based on the user input, one or more
adjustments to a control policy which controls electrical
stimulation delivered by a medical device based on at least one
evoked compound action potentials (ECAP) sensed by the medical
device.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 63/037,361, filed on Jun. 10, 2020, the
entire content of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] This disclosure generally relates to electrical stimulation
therapy, and more specifically, control of electrical stimulation
therapy.
BACKGROUND
[0003] Medical devices may be external or implanted and may be used
to deliver electrical stimulation therapy to patients via various
tissue sites to treat a variety of symptoms or conditions such as
chronic pain, tremor, Parkinson's disease, epilepsy, urinary or
fecal incontinence, sexual dysfunction, obesity, or gastroparesis.
A medical device may deliver electrical stimulation therapy via one
or more leads that include electrodes located proximate to target
locations associated with the brain, the spinal cord, pelvic
nerves, peripheral nerves, or the gastrointestinal tract of a
patient. Stimulation proximate the spinal cord, proximate the
sacral nerve, within the brain, and proximate peripheral nerves are
often referred to as spinal cord stimulation (SCS), sacral
neuromodulation (SNM), deep brain stimulation (DBS), and peripheral
nerve stimulation (PNS), respectively.
[0004] An evoked compound action potential (ECAP) is synchronous
firing of a population of neurons which occurs in response to the
application of a stimulus including, in some cases, an electrical
stimulus by a medical device. The ECAP may be detectable as being a
separate event from the stimulus itself, and the ECAP may reveal
characteristics of the effect of the stimulus on the nerve fibers.
Electrical stimulation may be delivered to a patient by the medical
device in a train of electrical pulses, and parameters of the
electrical pulses may include a frequency, an amplitude, a pulse
width, and a pulse shape. The parameters of the electrical pulses
may be altered in response to sensory input, such as ECAPs sensed
in response to the train of electrical pulses. Such alterations may
affect the patient's perception of the electrical pulses, or lack
thereof.
SUMMARY
[0005] In general, the disclosure is directed to devices, systems,
and techniques for controlling electrical stimulation therapy. For
example, a medical device may control a level of electrical
stimulation based on sensing a plurality of evoked compound action
potentials (ECAPs). The medical device, in some cases, may reduce
an intensity of stimulation pulses in response to a characteristic
of a detected ECAP signal exceeding a threshold ECAP value and
subsequently increase the intensity of stimulation pulses after the
characteristic of later ECAP signals dropping back below the
threshold ECAP value. It may be beneficial to change a control
policy that define the electrical stimulation in order to account
for movement (e.g., one or both of both short-term and long-term
migration) of electrodes coupled to the medical device. More
specifically, techniques of this disclosure may allow processing
circuitry to execute an algorithm for changing (e.g., automatically
changing or recommending user changes) the control policy which
determines how the medical device changes parameter values that
define the electrical stimulation.
[0006] The control policy may be established when initiating
therapy for the patient, changed periodically over time, or changed
in response to a trigger event. The control policy may decrease a
likelihood that the stimulation causes a patient to experience an
uncomfortable sensation, e.g., "transient overstimulation," and may
decrease a likelihood that the stimulation causes the patient to
experience a reduced therapeutic benefit. The parameters defining
the control policy may similarly need to be first established and
then adjusted over time in order to maintain effective therapeutic
benefit and reduce the likelihood of undesired stimulation. The
medical device or external device associated with the medical
device may execute an algorithm that elicits responses from a user
and determines adjustments to the parameters that define the
control policy based on the user responses.
[0007] Additionally, one or more techniques of this disclosure
include receiving and analyzing ECAP data corresponding to an event
indicated by a patient, where the ECAP data may be a factor in
determining recommended changes to the control policy. For example,
the medical device may capture ECAP data corresponding to a period
of time responsive to receiving patient input indicating an
occurrence of an event, the period of time including the occurrence
of the event. The medical device may output the ECAP data in a
certain format, such as a histogram, for later analysis. A device
may use the captured ECAP data in order to recommend one or more
changes to the control policy or determine whether to prompt the
patient for information that is useful for making one or more
changes to the control policy.
[0008] In some examples, a system includes a user interface; and
processing circuitry. The processing circuitry is configured to
output, for display by the user interface, a message requesting the
patient perform a set of actions, receive, from the user interface,
user input indicative of a patient response associated with the set
of actions, and determine, based on the user input, one or more
adjustments to a control policy which controls electrical
stimulation delivered by a medical device based on at least one
evoked compound action potentials (ECAP) sensed by the medical
device.
[0009] In some examples, a method includes outputting, by
processing circuitry for display by the user interface, a message
requesting the patient perform a set of actions, receiving, by the
processing circuitry from the user interface, user input indicative
of a patient response associated with the set of actions, and
determining, by the processing circuitry based on the user input,
one or more adjustments to a control policy which controls
electrical stimulation delivered by a medical device based on at
least one evoked compound action potentials (ECAP) sensed by the
medical device.
[0010] In some examples, a computer-readable medium includes
instructions that, when executed by a processor, causes the
processor to output, for display by the user interface, a message
requesting the patient perform a set of actions, receive, from the
user interface, user input indicative of a patient response
associated with the set of actions, and determine, based on the
user input, one or more adjustments to a control policy which
controls electrical stimulation delivered by a medical device based
on at least one evoked compound action potentials (ECAP) sensed by
the medical device.
[0011] In some examples, a medical device includes stimulation
generation circuitry configured to deliver electrical stimulation
to a patient, where the electrical stimulation therapy includes a
plurality of stimulation pulses; sensing circuitry configured to
sense one or more evoked compound action potentials (ECAPs), where
the sensing circuitry is configured to sense each ECAP of the one
or more ECAPs elicited by a respective stimulation pulse of the
plurality of stimulation pulses; and processing circuitry
configured to store a set of histogram data corresponding to a set
of ECAPs of the plurality of ECAPs, the set of ECAPs being sensed
by the sensing circuitry over a window of time.
[0012] In some examples, a method includes delivering, by
stimulation generation circuitry, electrical stimulation to a
patient, where the electrical stimulation therapy includes a
plurality of stimulation pulses, sensing, by sensing circuitry, one
or more evoked compound action potentials (ECAPs), where the
sensing circuitry is configured to sense each ECAP of the one or
more ECAPs elicited by a respective stimulation pulse of the
plurality of stimulation pulses. and storing, by processing
circuitry, a set of histogram data corresponding to a set of ECAPs
of the plurality of ECAPs, the set of ECAPs being sensed by the
sensing circuitry over a window of time.
[0013] In some examples, a computer-readable medium includes
instructions that, when executed by a processor, causes the
processor to deliver electrical stimulation to a patient, where the
electrical stimulation therapy includes a plurality of stimulation
pulses, sense one or more evoked compound action potentials
(ECAPs), where the sensing circuitry is configured to sense each
ECAP of the one or more ECAPs elicited by a respective stimulation
pulse of the plurality of stimulation pulses, and store a set of
histogram data corresponding to a set of ECAPs of the plurality of
ECAPs, the set of ECAPs being sensed by the sensing circuitry over
a window of time.
[0014] The summary is intended to provide an overview of the
subject matter described in this disclosure. It is not intended to
provide an exclusive or exhaustive explanation of the systems,
device, and methods described in detail within the accompanying
drawings and description below. Further details of one or more
examples of this disclosure are set forth in the accompanying
drawings and in the description below. Other features, objects, and
advantages will be apparent from the description and drawings, and
from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a conceptual diagram illustrating an example
system that includes an implantable medical device (IMD) configured
to deliver spinal cord stimulation (SCS) therapy and an external
programmer, in accordance with one or more techniques of this
disclosure.
[0016] FIG. 2 is a block diagram illustrating an example
configuration of components of an IMD, in accordance with one or
more techniques of this disclosure.
[0017] FIG. 3 is a block diagram illustrating an example
configuration of components of an external programmer, in
accordance with one or more techniques of this disclosure.
[0018] FIG. 4 is a graph of example evoked compound action
potentials (ECAPs) sensed for respective stimulation pulses, in
accordance with one or more techniques of this disclosure.
[0019] FIG. 5A is a timing diagram illustrating an example of
electrical stimulation pulses, respective stimulation signals, and
respective sensed ECAPs, in accordance with one or more techniques
of this disclosure.
[0020] FIG. 5B is a timing diagram illustrating one example of
electrical stimulation pulses, respective stimulation signals, and
respective sensed ECAPs, in accordance with one or more techniques
of this disclosure.
[0021] FIG. 6A is a timing diagram illustrating an example of
electrical stimulation pulses, respective stimulation signals, and
respective sensed ECAPs, in accordance with one or more techniques
of this disclosure.
[0022] FIG. 6B is a timing diagram illustrating another example of
electrical stimulation pulses, respective stimulation signals, and
respective sensed ECAPs, in accordance with one or more techniques
of this disclosure.
[0023] FIG. 7 is a timing diagram illustrating another example of
electrical stimulation pulses, respective stimulation signals, and
respective ECAPs, in accordance with one or more techniques of this
disclosure.
[0024] FIG. 8 is a timing diagram illustrating another example of
electrical stimulation pulses, respective stimulation signals, and
respective ECAPs, in accordance with one or more techniques of this
disclosure.
[0025] FIG. 9 is a flow diagram illustrating an example operation
for controlling stimulation based on one or more sensed ECAPs, in
accordance with one or more techniques of this disclosure.
[0026] FIG. 10 illustrates a voltage/current/time graph which plots
control pulse current amplitude, informed pulse current amplitude,
ECAP voltage amplitude, and second ECAP voltage amplitude as a
function of time, in accordance with one or more techniques of this
disclosure.
[0027] FIG. 11 is a flow diagram illustrating an example operation
for controlling stimulation based on one or more sensed ECAPs, in
accordance with one or more techniques of this disclosure.
[0028] FIG. 12 illustrates a voltage/current/time graph which plots
control pulse current amplitude, informed pulse current amplitude,
and ECAP voltage amplitude as a function of time, in accordance
with one or more techniques of this disclosure.
[0029] FIG. 13 is a block diagram illustrating a system for
determining a control policy of an IMD, in accordance with one or
more techniques of this disclosure.
[0030] FIG. 14 is a flow diagram illustrating an example operation
for adjusting a control policy for the IMD of FIG. 1, in accordance
with one or more techniques of this disclosure.
[0031] FIG. 15 is a flow diagram illustrating an example operation
for generating a recommendation for controlling one or more therapy
parameters, in accordance with one or more techniques of this
disclosure.
[0032] FIG. 16 is a flow diagram illustrating an example operation
for outputting one or more requests and receiving one or more
responses in order to adjust stimulation to a patient by the IMD of
FIG. 1, in accordance with one or more techniques of this
disclosure.
[0033] FIGS. 17A-17B are flow diagrams illustrating an example
operation for outputting one or more requests and receiving one or
more responses, in accordance with one or more techniques of this
disclosure.
[0034] FIG. 18 is a flow diagram illustrating an example for saving
one or more sets of histogram data, in accordance with one or more
techniques of this disclosure.
[0035] FIG. 19 is a graph illustrating ECAP amplitudes of a set of
ECAPs sensed by the IMD of FIG. 1, in accordance with one or more
techniques of this disclosure.
[0036] FIG. 20 is a graph which illustrates histogram data
including a set of histograms corresponding to the data of the
graph of FIG. 19, in accordance with one or more techniques of this
disclosure.
[0037] Like reference characters denote like elements throughout
the description and figures.
DETAILED DESCRIPTION
[0038] The disclosure describes examples of medical devices,
systems, and techniques for setting or adjusting parameters that
define a control policy employed by a medical device to make
automatic adjustments to stimulation parameters that define
electrical stimulation. A medical device may thus automatically
adjust electrical stimulation therapy delivered to a patient based
on the control policy and one or more characteristics of evoked
compound action potentials (ECAPs) received by a medical device.
This disclosure describes one or more techniques for adjusting a
control policy that the medical device employs to adjust
stimulation parameter values that define the electrical stimulation
therapy. Electrical stimulation therapy is typically delivered to a
target tissue (e.g., one or more nerves or muscle) of a patient via
two or more electrodes. Parameters of the electrical stimulation
therapy (e.g., electrode combination, voltage or current amplitude,
pulse width, pulse frequency, etc.) are selected by a clinician
and/or the patient to provide relief from various symptoms, such as
pain, muscle disorders, etc.
[0039] However, as the patient moves, the distance between the
electrodes and the target tissues changes. Posture changes or
patient activity can cause electrodes to move closer or farther
from target nerves. Lead migration over time may also change this
distance between electrodes and target tissue. In some examples,
transient patient conditions such as coughing, sneezing, laughing,
Valsalva maneuvers, leg lifting, cervical motions, or deep
breathing may temporarily cause the stimulation electrodes of the
medical device to move closer to the target tissue of the patient,
intermittently changing the patient's perception of electrical
stimulation therapy.
[0040] Since neural recruitment is a function of stimulation
intensity and distance between the target tissue and the
electrodes, movement of the electrode closer to the target tissue
may result in increased perception by the patient (e.g., possible
uncomfortable, undesired, or painful sensations), and movement of
the electrode further from the target tissue may result in
decreased efficacy of the therapy for the patient. For example, if
stimulation is held consistent and the stimulation electrodes are
moved closer to the target tissue, the patient may perceive the
stimulation as more intense, uncomfortable, or even painful.
Conversely, consistent stimulation while electrodes are moved
farther from target tissue may result in the patient perceiving
less intense stimulation which may reduce the therapeutic effect
for the patient. Discomfort or pain caused by transient patient
conditions may be referred to herein as "transient
overstimulation." Therefore, in some examples, it may be beneficial
to adjust stimulation parameters in response to patent movement or
other conditions that can cause transient overstimulation.
[0041] An ECAP may be evoked by a stimulation pulse delivered to
nerve fibers of the patient. After being evoked, the ECAP may
propagate down the nerve fibers away from the initial stimulus.
Sensing circuitry of the medical device may, in some cases, detect
this ECAP. Characteristics of the detected ECAP signal may indicate
the distance between electrodes and target tissue is changing. For
example, a sharp increase in ECAP amplitude over a short period of
time (e.g., less than one second) may indicate that the distance
between the electrodes and the target tissue is decreasing due to a
transient patient action such as a cough. A gradual increase in
ECAP amplitude over a longer period of time (e.g., days, weeks, or
months) may indicate that the distance between the electrodes and
the target tissue is decreasing due to long-term lead migration
after the medical device is implanted. It may be beneficial to
adjust one or more therapy parameter values in order to prevent the
patient from experiencing uncomfortable sensations due to one or
both of short-term movement of the electrodes relative to the
target tissue and long-term movement of the electrodes relative to
the target tissue.
[0042] In order to facilitate the sensing of ECAPs, in some
examples, the medical device can deliver pulses as part of a
therapy (e.g., informed pulses) and also deliver a plurality of
control pulses that are designed to elicit detectable ECAPs when
the informed pulses do not elicit detectable ECAPs. For example,
the control pulse duration may be shorter than the informed pulse
to reduce or eliminate the signal artifact that is caused by the
informed pulse and prevents or limited detection of the ECAP
received at a sensing electrodes). In particular embodiments, the
control pulse is short enough that the pulse ends prior to the
arrival of all, or most, of the ECAP signal at the sensing
electrode(s). In this manner, the medical device may interleave the
plurality of control pulses with at least some informed pulses of
the plurality of informed pulses. For example, the medical device
may deliver informed pulses for a period of time before delivering
a control pulse and sensing the corresponding ECAP (if any). The
medical device can then resume delivery of the informed pulses for
another period of time. In some examples, a pulse duration of the
control pulses is less than a pulse duration of the informed pulses
and the pulse duration of the control pulses is short enough so
that the medical device can sense an individual ECAP for each
control pulse. In some examples, the control pulses may provide or
contribute to the therapy perceived by the patient.
[0043] As described herein, transient patient actions may cause a
distance between the electrodes and the target tissue to
temporarily change during the respective transient patient action.
This transient patient action may include one or more quick
movements on the order of seconds or less. During this transient
movement, the distance between the electrodes and the target tissue
may change and affect the patient's perception of the electrical
stimulation therapy delivered by the medical device. If stimulation
pulses are constant and the electrodes move closer to the target
tissue, the patient may experience a greater or heightened
"feeling" or sensation from the therapy. This heightened feeling
may be perceived as discomfort or pain (e.g., transient
overstimulation) in response to the electrodes moving closer to the
target tissue. ECAPs are a measure of neural recruitment because
each ECAP signal represents the superposition of electrical
potentials generated from axons firing in response to an electrical
stimulus (e.g., a stimulation pulse). Changes in a characteristic
(e.g., an amplitude of a portion of the signal) of an ECAP signal
occurs as a function of how many axons have been activated by the
delivered stimulation pulse.
[0044] Since ECAPs may provide an indication of the patient's
perception of the electrical stimulation therapy, techniques of
this disclosure may enable the medical device to decrease one or
more parameters of stimulation pulses delivered to the target
tissue in response to a first ECAP exceeding a threshold ECAP
characteristic value. By decreasing the one or more parameters of
the informed pulses, the medical device may prevent the patient
from experiencing transient overstimulation. Subsequently, if the
medical device determines that sensed ECAPs have later fallen below
the threshold ECAP characteristic value, the medical device may
restore the stimulation pulses to parameter values that were set
before the medical device decreased the one or more parameters of
the stimulation pulses in response to the exceeded threshold ECAP
characteristic value.
[0045] The techniques of this disclosure may provide one or more
advantages. For example, it may be beneficial to change the rate at
which the medical device decreases and subsequently increases the
one or more parameters of the stimulation pulses delivered to the
target tissue in response to a transient patient action or in
response to a change in control policy. For example, processing
circuitry may execute an algorithm which generates one or more
recommendations or automatically changes one or more parameters
that define a control policy which controls how the medical device
changes stimulation parameters based on a physiological signal such
as an ECAP characteristic value. Based on receiving an indication
that the patient experienced transient overstimulation at a
beginning of a transient patient action, the processing circuitry
may increase the rate at which the medical device decreases one or
more stimulation parameters defining the stimulation pulses
responsive to the first ECAP exceeding the threshold ECAP
characteristic value. Additionally, or alternatively, based on
receiving an indication that the patient experienced transient
overstimulation at an end of a transient patient action, the
processing circuitry may decrease the rate at which the medical
device increases one or more parameters of the stimulation pulses
following a decrease in the one or more parameters responsive to
the first ECAP exceeding the threshold ECAP characteristic value.
Instead of automatically adjusting the parameters of the control
policy, the system may generate a recommendation to be presented to
a user indicating an appropriate adjustment to the control policy.
In this manner a user, such as a clinician or a patient, can accept
or confirm the recommended change in some examples.
[0046] It may be beneficial to execute an algorithm to output a set
of prompts for display to a user interface of an external device,
enabling a patient to provide a set of responses indicating aspects
of one or more sensations experienced by the patient. For example,
the set of prompts may include a prompt for the patient to perform
an action. Additionally, the set of prompts may include one or more
prompts for the patient to characterize one or more sensations
before, during, or after the action performed by the patient. Based
on the set of responses, processing circuitry may execute the
algorithm to provide one or more changes to the control policy that
determines adjustments to stimulation parameters defining therapy
delivered to the target tissue. The processing circuitry may
automatically change the one or more parameters of the control
policy based on the recommendation, but this is not required.
[0047] Additionally, the medical device may capture histogram data
for analysis. The histogram data, in some examples, may include one
or more sets of histograms, where each histogram of the one or more
sets of histograms includes a set of bins. A histogram may include
a plurality of ECAP amplitudes measured by the medical device over
a period of time. A set of histograms may represent a sequence of
histograms each corresponding to a period of time (e.g., one
second). That is, a first histogram may correspond to a first
period of time, a second histogram may correspond to a second
period of time directly following the first period of time, a third
histogram may correspond to a third period of time directly
following the second period of time, and so on. Each histogram of
the sequence of histograms may include a set of "bins," where each
bin of the set of bins corresponds to a range of ECAP amplitudes.
In this way, the medical device or user may identify the quantity
of times that the patient may have experienced transient
overstimulation based on the histograms and a sequence of
histograms over time.
[0048] The medical device may capture each set of histograms of the
one or more sets of histograms based on one or more triggers. For
example, the medical device may capture at least one set of
histograms of the one or more sets of histograms based on receiving
an instruction to capture a set of histograms, the medical device
may capture at least one set of histograms of the one or more sets
of histograms based on detecting one or more events which trigger
the medical device to capture a set of histograms, the medical
device may capture at least one set of histograms of the one or
more sets of histograms based on a schedule (e.g., daily, hourly,
or any other time interval), or any combination thereof. The
medical device may save each set of histograms of the one or more
sets of histograms to a memory, where each of set of histograms of
the one or more sets of histograms is associated with a timestamp.
In this way, processing circuitry may analyze the sets of
histograms and the associated timestamps when determining control
policy in order to adjust the control policy to improve detection
of overstimulation events.
[0049] In some examples, the medical device may deliver stimulation
that includes pulses (e.g., control pulses) that contribute to
therapy and also elicit detectable ECAP signals. In other examples,
the medical device may deliver the stimulation pulses to include
control pulses and informed pulses. Nerve impulses detectable as
the ECAP signal travel quickly along the nerve fiber after the
delivered stimulation pulse first depolarizes the nerve. Therefore,
if the stimulation pulse delivered by first electrodes has a pulse
width that is too long, different electrodes configured to sense
the ECAP will sense the stimulation pulse itself as an artifact
that obscures the lower amplitude ECAP signal. However, the ECAP
signal loses fidelity as the electrical potentials propagate from
the electrical stimulus because different nerve fibers propagate
electrical potentials at different speeds. Therefore, sensing the
ECAP at a far distance from the stimulating electrodes may avoid
the artifact caused by a stimulation pulse with a long pulse width,
but the ECAP signal may lose fidelity needed to detect changes to
the ECAP signal that occur when the electrode to target tissue
distance changes. In other words, the system may not be able to
identify, at any distance from the stimulation electrodes, ECAPs
from stimulation pulses configured to provide a therapy to the
patient. Therefore, the medical device may employ control pulses
configured to elicit detectable ECAPs and informed pulses that may
contribute to therapeutic effects for the patient by may not elicit
detectable ECAPs.
[0050] In these examples, a medical device is configured to deliver
a plurality of informed pulses configured to provide a therapy to
the patient and a plurality of control pulses that may or may not
contribute to therapy. At least some of the control pulses may
elicit a detectable ECAP signal without the primary purpose of
providing a therapy to the patient. The control pulses may be
interleaved with the delivery of the informed pulses. For example,
the medical device may alternate the delivery of informed pulses
with control pulses such that a control pulse is delivered, and an
ECAP signal is sensed, between consecutive informed pulses. In some
examples, multiple control pulses are delivered, and respective
ECAP signals sensed, between the delivery of consecutive informed
pulses. In some examples, multiple informed pulses will be
delivered between consecutive control pulses. In any case, the
informed pulses may be delivered according to a predetermined pulse
frequency selected so that the informed pulses can produce a
therapeutic result for the patient. One or more control pulses are
then delivered, and the respective ECAP signals sensed, within one
or more time windows between consecutive informed pulses delivered
according to the predetermined pulse frequency. In this manner, a
medical device can deliver informed pulses from the medical device
uninterrupted while ECAPs are sensed from control pulses delivered
during times at which the informed pulses are not being delivered.
In other examples described herein, ECAPs are sensed by the medical
device in response to the informed pulses delivered by the medical
device, and control pulses are not used to elicit ECAPs.
[0051] According to the examples described herein, a medical device
may be configured to deliver stimulation pulses as including
control pulses or a combination of a plurality of control pulses
and a plurality of informed pulses. The plurality of control
pulses, in some cases, may be therapeutic and contribute to therapy
received by the patient. In other examples, the plurality of the
control pulses may be non-therapeutic and not contribute to the
therapy received by the patient. Put another way, the control
pulses configured to elicit detectable ECAPs may or may not
contribute to alleviating the patient's condition or symptoms of
the patient's condition. In contrast to control pulses, informed
pulses may not elicit a detectable ECAP or the system may not
utilize ECAPs from informed pulses as feedback to control therapy.
Therefore, the medical device or other component associated with
the medical device may determine values of one or more stimulation
parameters that at least partially define the informed pulses based
on an ECAP signal elicited by a control pulse instead. In this
manner, the informed pulse may be informed by the ECAP elicited
from a control pulse. The medical device or other component
associated with the medical device may determine values of one or
more stimulation parameters that at least partially define the
control pulses based on an ECAP signal elicited by previous control
pulse.
[0052] Although electrical stimulation is generally described
herein in the form of electrical stimulation pulses, electrical
stimulation may be delivered in non-pulse form in other examples.
For example, electrical stimulation may be delivered as a signal
having various waveform shapes, frequencies, and amplitudes.
Therefore, electrical stimulation in the form of a non-pulse signal
may be a continuous signal than may have a sinusoidal waveform or
other continuous waveform.
[0053] FIG. 1 is a conceptual diagram illustrating an example
system 100 that includes an implantable medical device (IMD) 110
configured to deliver spinal cord stimulation (SCS) therapy and an
external programmer 150, in accordance with one or more techniques
of this disclosure. Although the techniques described in this
disclosure are generally applicable to a variety of medical devices
including external devices and IMDs, application of such techniques
to IMDs and, more particularly, implantable electrical stimulators
(e.g., neurostimulators) will be described for purposes of
illustration. More particularly, the disclosure will refer to an
implantable SCS system for purposes of illustration, but without
limitation as to other types of medical devices or other
therapeutic applications of medical devices.
[0054] As shown in FIG. 1, system 100 includes an IMD 110, leads
130A and 130B, and external programmer 150 shown in conjunction
with a patient 105, who is ordinarily a human patient. In the
example of FIG. 1, IMD 110 is an implantable electrical stimulator
that is configured to generate and deliver electrical stimulation
therapy to patient 105 via one or more electrodes of electrodes of
leads 130A and/or 130B (collectively, "leads 130"), e.g., for
relief of chronic pain or other symptoms. In other examples, IMD
110 may be coupled to a single lead carrying multiple electrodes or
more than two leads each carrying multiple electrodes. As a part of
delivering stimulation pulses of the electrical stimulation
therapy, IMD 110 may be configured to generate and deliver control
pulses configured to elicit ECAP signals. The control pulses may
provide therapy in some examples. In other examples, IMD 110 may
deliver informed pulses that contribute to the therapy for the
patient, but which do not elicit detectable ECAPs. IMD 110 may be a
chronic electrical stimulator that remains implanted within patient
105 for weeks, months, or even years. In other examples, IMD 110
may be a temporary, or trial, stimulator used to screen or evaluate
the efficacy of electrical stimulation for chronic therapy. In one
example, IMD 110 is implanted within patient 105, while in another
example, IMD 110 is an external device coupled to percutaneously
implanted leads. In some examples, IMD 110 uses one or more leads,
while in other examples, IMD 110 is leadless.
[0055] IMD 110 may be constructed of any polymer, metal, or
composite material sufficient to house the components of IMD 110
(e.g., components illustrated in FIG. 2) within patient 105. In
this example, IMD 110 may be constructed with a biocompatible
housing, such as titanium or stainless steel, or a polymeric
material such as silicone, polyurethane, or a liquid crystal
polymer, and surgically implanted at a site in patient 105 near the
pelvis, abdomen, or buttocks. In other examples, IMD 110 may be
implanted within other suitable sites within patient 105, which may
depend, for example, on the target site within patient 105 for the
delivery of electrical stimulation therapy. The outer housing of
IMD 110 may be configured to provide a hermetic seal for
components, such as a rechargeable or non-rechargeable power
source. In addition, in some examples, the outer housing of IMD 110
is selected from a material that facilitates receiving energy to
charge the rechargeable power source.
[0056] Electrical stimulation energy, which may be constant current
or constant voltage-based pulses, for example, is delivered from
IMD 110 to one or more target tissue sites of patient 105 via one
or more electrodes (not shown) of implantable leads 130. In the
example of FIG. 1, leads 130 carry electrodes that are placed
adjacent to the target tissue of spinal cord 120. One or more of
the electrodes may be disposed at a distal tip of a lead 130 and/or
at other positions at intermediate points along the lead. Leads 130
may be implanted and coupled to IMD 110. The electrodes may
transfer electrical stimulation generated by an electrical
stimulation generator in IMD 110 to tissue of patient 105. Although
leads 130 may each be a single lead, lead 130 may include a lead
extension or other segments that may aid in implantation or
positioning of lead 130. In some other examples, IMD 110 may be a
leadless stimulator with one or more arrays of electrodes arranged
on a housing of the stimulator rather than leads that extend from
the housing. In addition, in some other examples, system 100 may
include one lead or more than two leads, each coupled to IMD 110
and directed to similar or different target tissue sites.
[0057] The electrodes of leads 130 may be electrode pads on a
paddle lead, circular (e.g., ring) electrodes surrounding the body
of the lead, conformable electrodes, cuff electrodes, segmented
electrodes (e.g., electrodes disposed at different circumferential
positions around the lead instead of a continuous ring electrode),
any combination thereof (e.g., ring electrodes and segmented
electrodes) or any other type of electrodes capable of forming
unipolar, bipolar or multipolar electrode combinations for therapy.
Ring electrodes arranged at different axial positions at the distal
ends of lead 130 will be described for purposes of
illustration.
[0058] The deployment of electrodes via leads 130 is described for
purposes of illustration, but arrays of electrodes may be deployed
in different ways. For example, a housing associated with a
leadless stimulator may carry arrays of electrodes, e.g., rows
and/or columns (or other patterns), to which shifting operations
may be applied. Such electrodes may be arranged as surface
electrodes, ring electrodes, or protrusions. As a further
alternative, electrode arrays may be formed by rows and/or columns
of electrodes on one or more paddle leads. In some examples,
electrode arrays include electrode segments, which are arranged at
respective positions around a periphery of a lead, e.g., arranged
in the form of one or more segmented rings around a circumference
of a cylindrical lead. In other examples, one or more of leads 130
are linear leads having 8 ring electrodes along the axial length of
the lead. In another example, the electrodes are segmented rings
arranged in a linear fashion along the axial length of the lead and
at the periphery of the lead.
[0059] The stimulation parameter of a therapy stimulation program
that defines the stimulation pulses of electrical stimulation
therapy by IMD 110 through the electrodes of leads 130 may include
information identifying which electrodes have been selected for
delivery of stimulation according to a stimulation program, the
polarities of the selected electrodes, i.e., the electrode
combination for the program, and voltage or current amplitude,
pulse frequency, pulse width, pulse shape of stimulation delivered
by the electrodes. These stimulation parameters of stimulation
pulses (e.g., control pulses and/or informed pulses) are typically
predetermined parameter values determined prior to delivery of the
stimulation pulses (e.g., set according to a stimulation program).
However, in some examples, system 100 changes one or more parameter
values automatically based on one or more factors or based on user
input and/or the control policy.
[0060] An ECAP test stimulation program may define stimulation
parameter values that define control pulses delivered by IMD 110
through at least some of the electrodes of leads 130. These
stimulation parameter values may include information identifying
which electrodes have been selected for delivery of control pulses,
the polarities of the selected electrodes, i.e., the electrode
combination for the program, and voltage or current amplitude,
pulse frequency, pulse width, and pulse shape of stimulation
delivered by the electrodes. The stimulation signals (e.g., one or
more stimulation pulses or a continuous stimulation waveform)
defined by the parameters of each ECAP test stimulation program are
configured to evoke a compound action potential from nerves. In
some examples, the ECAP test stimulation program defines when the
control pulses are to be delivered to the patient based on the
frequency and/or pulse width of the informed pulses when informed
pulse are also delivered. In some examples, the stimulation defined
by each ECAP test stimulation program are not intended to provide
or contribute to therapy for the patient. In other examples, the
stimulation defined by each ECAP test stimulation program may
contribute to therapy when the control pulses elicit detectable
ECAP signals and contribute to therapy. In this manner, the ECAP
test stimulation program may define stimulation parameters the same
or similar to the stimulation parameters of therapy stimulation
programs.
[0061] Although FIG. 1 is directed to SCS therapy, e.g., used to
treat pain, in other examples system 100 may be configured to treat
any other condition that may benefit from electrical stimulation
therapy. For example, system 100 may be used to treat tremor,
Parkinson's disease, epilepsy, a pelvic floor disorder (e.g.,
urinary incontinence or other bladder dysfunction, fecal
incontinence, pelvic pain, bowel dysfunction, or sexual
dysfunction), obesity, gastroparesis, or psychiatric disorders
(e.g., depression, mania, obsessive compulsive disorder, anxiety
disorders, and the like). In this manner, system 100 may be
configured to provide therapy taking the form of deep brain
stimulation (DBS), peripheral nerve stimulation (PNS), peripheral
nerve field stimulation (PNFS), cortical stimulation (CS), pelvic
floor stimulation, gastrointestinal stimulation, or any other
stimulation therapy capable of treating a condition of patient
105.
[0062] In some examples, lead 130 includes one or more sensors
configured to allow IMD 110 to monitor one or more parameters of
patient 105, such as patient activity, pressure, temperature, or
other characteristics. The one or more sensors may be provided in
addition to, or in place of, therapy delivery by lead 130.
[0063] IMD 110 is configured to deliver electrical stimulation
therapy to patient 105 via selected combinations of electrodes
carried by one or both of leads 130, alone or in combination with
an electrode carried by or defined by an outer housing of IMD 110.
The target tissue for the electrical stimulation therapy may be any
tissue affected by electrical stimulation, which may be in the form
of electrical stimulation pulses or continuous waveforms. In some
examples, the target tissue includes nerves, smooth muscle or
skeletal muscle. In the example illustrated by FIG. 1, the target
tissue is tissue proximate spinal cord 120, such as within an
intrathecal space or epidural space of spinal cord 120, or, in some
examples, adjacent nerves that branch off spinal cord 120. Leads
130 may be introduced into spinal cord 120 in via any suitable
region, such as the thoracic, cervical or lumbar regions.
Stimulation of spinal cord 120 may, for example, prevent pain
signals from traveling through spinal cord 120 and to the brain of
patient 105. Patient 105 may perceive the interruption of pain
signals as a reduction in pain and, therefore, efficacious therapy
results. In other examples, stimulation of spinal cord 120 may
produce paresthesia which may be reduce the perception of pain by
patient 105, and thus, provide efficacious therapy results.
[0064] IMD 110 generates and delivers electrical stimulation
therapy to a target stimulation site within patient 105 via the
electrodes of leads 130 to patient 105 according to one or more
therapy stimulation programs. A therapy stimulation program defines
values for one or more parameters that define an aspect of the
therapy delivered by IMD 110 according to that program. For
example, a therapy stimulation program that controls delivery of
stimulation by IMD 110 in the form of pulses may define values for
voltage or current pulse amplitude, pulse width, and pulse rate
(e.g., pulse frequency) for stimulation pulses delivered by IMD 110
according to that program.
[0065] In some examples where ECAP signals cannot be detected from
the types of pulses intended to be delivered to provide therapy to
the patient, control pulses and informed pulses may be delivered.
For example, IMD 110 is configured to deliver control stimulation
to patient 105 via a combination of electrodes of leads 130, alone
or in combination with an electrode carried by or defined by an
outer housing of IMD 110. The tissue targeted by the control
stimulation may be the same tissue targeted by the electrical
stimulation therapy, but IMD 110 may deliver control stimulation
pulses via the same, at least some of the same, or different
electrodes. Since control stimulation pulses are delivered in an
interleaved manner with informed pulses, a clinician and/or user
may select any desired electrode combination for informed pulses.
Like the electrical stimulation therapy, the control stimulation
may be in the form of electrical stimulation pulses or continuous
waveforms. In one example, each control stimulation pulse may
include a balanced, bi-phasic square pulse that employs an active
recharge phase. However, in other examples, the control stimulation
pulses may include a monophasic pulse followed by a passive
recharge phase. In other examples, a control pulse may include an
imbalanced bi-phasic portion and a passive recharge portion.
Although not necessary, a bi-phasic control pulse may include an
interphase interval between the positive and negative phase to
promote propagation of the nerve impulse in response to the first
phase of the bi-phasic pulse. The control stimulation may be
delivered without interrupting the delivery of the electrical
stimulation informed pulses, such as during the window between
consecutive informed pulses. The control pulses may elicit an ECAP
signal from the tissue, and IMD 110 may sense the ECAP signal via
two or more electrodes on leads 130. In cases where the control
stimulation pulses are applied to spinal cord 120, the signal may
be sensed by IMD 110 from spinal cord 120.
[0066] IMD 110 may deliver control stimulation to a target
stimulation site within patient 105 via the electrodes of leads 130
according to one or more ECAP test stimulation programs. The one or
more ECAP test stimulation programs may be stored in a storage
device of IMD 110. Each ECAP test program of the one or more ECAP
test stimulation programs includes values for one or more
parameters that define an aspect of the control stimulation
delivered by IMD 110 according to that program, such as current or
voltage amplitude, pulse width, pulse frequency, electrode
combination, and, in some examples timing based on informed pulses
to be delivered to patient 105. In some examples, IMD 110 delivers
control stimulation to patient 105 according to multiple ECAP test
stimulation programs.
[0067] A user, such as a clinician or patient 105, may interact
with a user interface of an external programmer 150 to program IMD
110. Programming of IMD 110 may refer generally to the generation
and transfer of commands, programs, or other information to control
the operation of IMD 110. In this manner, IMD 110 may receive the
transferred commands and programs from external programmer 150 to
control electrical stimulation therapy (e.g., informed pulses) and
control stimulation (e.g., control pulses). For example, external
programmer 150 may transmit therapy stimulation programs, ECAP test
stimulation programs, stimulation parameter adjustments, therapy
stimulation program selections, ECAP test program selections, user
input, or other information to control the operation of IMD 110,
e.g., by wireless telemetry or wired connection. As described
herein, stimulation delivered to the patient may include control
pulses, and, in some examples, stimulation may include control
pulses and informed pulses.
[0068] In some cases, external programmer 150 may be characterized
as a physician or clinician programmer if it is primarily intended
for use by a physician or clinician. In other cases, external
programmer 150 may be characterized as a patient programmer if it
is primarily intended for use by a patient. A patient programmer
may be generally accessible to patient 105 and, in many cases, may
be a portable device that may accompany patient 105 throughout the
patient's daily routine. For example, a patient programmer may
receive input from patient 105 when the patient wishes to terminate
or change electrical stimulation therapy. In general, a physician
or clinician programmer may support selection and generation of
programs by a clinician for use by IMD 110, whereas a patient
programmer may support adjustment and selection of such programs by
a patient during ordinary use. In other examples, external
programmer 150 may include, or be part of, an external charging
device that recharges a power source of IMD 110. In this manner, a
user may program and charge IMD 110 using one device, or multiple
devices.
[0069] As described herein, information may be transmitted between
external programmer 150 and IMD 110. Therefore, IMD 110 and
external programmer 150 may communicate via wireless communication
using any techniques known in the art. Examples of communication
techniques may include, for example, radiofrequency (RF) telemetry
and inductive coupling, but other techniques are also contemplated.
In some examples, external programmer 150 includes a communication
head that may be placed proximate to the patient's body near the
IMD 110 implant site to improve the quality or security of
communication between IMD 110 and external programmer 150.
Communication between external programmer 150 and IMD 110 may occur
during power transmission or separate from power transmission.
[0070] In some examples, IMD 110, in response to commands from
external programmer 150, delivers electrical stimulation therapy
according to a plurality of therapy stimulation programs to a
target tissue site of the spinal cord 120 of patient 105 via
electrodes (not depicted) on leads 130. In some examples, IMD 110
modifies therapy stimulation programs as therapy needs of patient
105 evolve over time. For example, the modification of the therapy
stimulation programs may cause the adjustment of at least one
parameter of the plurality of informed pulses. When patient 105
receives the same therapy for an extended period, the efficacy of
the therapy may be reduced. In some cases, parameters of the
plurality of informed pulses may be automatically updated.
[0071] In this disclosure, efficacy of electrical stimulation
therapy may be indicated by one or more characteristics (e.g. an
amplitude of or between one or more peaks or an area under the
curve of one or more peaks) of an action potential that is evoked
by a stimulation pulse delivered by IMD 110 (i.e., a characteristic
of the ECAP signal). Electrical stimulation therapy delivery by
leads 130 of IMD 110 may cause neurons within the target tissue to
evoke a compound action potential that travels up and down the
target tissue, eventually arriving at sensing electrodes of IMD
110. Furthermore, control stimulation may also elicit at least one
ECAP, and ECAPs responsive to control stimulation may also be a
surrogate for the effectiveness of the therapy. The amount of
action potentials (e.g., number of neurons propagating action
potential signals) that are evoked may be based on the various
parameters of electrical stimulation pulses such as amplitude,
pulse width, frequency, pulse shape (e.g., slew rate at the
beginning and/or end of the pulse), etc. The slew rate may define
the rate of change of the voltage and/or current amplitude of the
pulse at the beginning and/or end of each pulse or each phase
within the pulse. For example, a very high slew rate indicates a
steep or even near vertical edge of the pulse, and a low slew rate
indicates a longer ramp up (or ramp down) in the amplitude of the
pulse. In some examples, these parameters contribute to an
intensity of the electrical stimulation. In addition, a
characteristic of the ECAP signal (e.g., an amplitude) may change
based on the distance between the stimulation electrodes and the
nerves subject to the electrical field produced by the delivered
control stimulation pulses.
[0072] In one example, each therapy pulse may have a pulse width
greater than approximately 300 .mu.s, such as between approximately
300 .mu.s and 1000 .mu.s (i.e., 1 millisecond) in some examples. At
these pulse widths, IMD 110 may not sufficiently detect an ECAP
signal because the therapy pulse is also detected as an artifact
that obscures the ECAP signal. If ECAPs are not adequately
recorded, then ECAPs arriving at IMD 110 cannot be compared to the
target ECAP characteristic (e.g. a target ECAP amplitude), and
electrical therapy stimulation cannot be altered according to
responsive ECAPs. When informed pulses have these longer pulse
widths, IMD 110 may deliver control stimulation in the form of
control pulses. The control pulses may have pulse widths of less
than approximately 300 .mu.s, such as a bi-phasic pulse with each
phase having a duration of approximately 100 .mu.s. Since the
control pulses may have shorter pulse widths than the informed
pulses, the ECAP signal may be sensed and identified following each
control pulse and used to inform IMD 110 about any changes that
should be made to the informed pulses (and control pulses in some
examples). In general, the term "pulse width" refers to the
collective duration of every phase, and interphase interval when
appropriate, of a single pulse. A single pulse includes a single
phase in some examples (i.e., a monophasic pulse) or two or more
phases in other examples (e.g., a bi-phasic pulse or a tri-phasic
pulse). The pulse width defines a period of time beginning with a
start time of a first phase of the pulse and concluding with an end
time of a last phase of the pulse (e.g., a biphasic pulse having a
positive phase lasting 100 .mu.s, a negative phase lasting 100
.mu.s, and an interphase interval lasting 30 .mu.s defines a pulse
width of 230 .mu.s). In another example, a control pulse may
include a positive phase lasting 90 .mu.s, a negative phase lasting
90 .mu.s, and an interphase interval lasting 30 .mu.s to define a
pulse width of 210 .mu.s In another example, a control pulse may
include a positive phase lasting 120 .mu.s, a negative phase
lasting 120 .mu.s, and an interphase interval lasting 30 .mu.s to
define a pulse width of 270 .mu.s.
[0073] As described, the example techniques for adjusting
stimulation parameter values for informed pulses are based on
comparing the value of a characteristic of a measured ECAP signal
to a target ECAP characteristic value. During delivery of control
stimulation pulses defined by one or more ECAP test stimulation
programs, IMD 110, via two or more electrodes interposed on leads
130, senses electrical potentials of tissue of the spinal cord 120
of patient 105 to measure the electrical activity of the tissue.
IMD 110 senses ECAPs from the target tissue of patient 105, e.g.,
with electrodes on one or more leads 130 and associated sense
circuitry. In some examples, IMD 110 receives a signal indicative
of the ECAP from one or more sensors, e.g., one or more electrodes
and circuitry, internal or external to patient 105. Such an example
signal may include a signal indicating an ECAP of the tissue of
patient 105. Examples of the one or more sensors include one or
more sensors configured to measure a compound action potential of
patient 105, or a physiological effect indicative of a compound
action potential. For example, to measure a physiological effect
indicative of a compound action potential, the one or more sensors
may be an accelerometer, a pressure sensor, a bending sensor, a
sensor configured to detect a posture of patient 105, or a sensor
configured to detect a respiratory function of patient 105. In this
manner, although the ECAP may be indicative of a posture change or
other patient action, other sensors may also detect similar posture
changes or movements using modalities separate from the ECAP.
However, in other examples, external programmer 150 receives a
signal indicating a compound action potential in the target tissue
of patient 105 and transmits a notification to IMD 110.
[0074] In the example techniques described in this disclosure, the
control stimulation parameters and the target ECAP characteristic
values may be initially set at the clinic but may be set and/or
adjusted at home by patient 105. Once the target ECAP
characteristic values are set, the example techniques allow for
automatic adjustment of therapy pulse parameters to maintain
consistent volume of neural activation and consistent perception of
therapy for the patient when the electrode-to-neuron distance
changes. The ability to change the stimulation parameter values may
also allow the therapy to have long term efficacy, with the ability
to keep the intensity of the stimulation (e.g., as indicated by the
ECAP) consistent by comparing the measured ECAP values to the
target ECAP characteristic value. IMD 110 may perform these changes
without intervention by a physician or patient 105.
[0075] In some examples, the system changes the target ECAP
characteristic value over a period of time. The system may be
programmed to change the target ECAP characteristic in order to
adjust the intensity of informed pulses to provide varying
sensations to the patient (e.g., increase or decrease the volume of
neural activation). In one example, a system may be programmed to
oscillate a target ECAP characteristic value between a maximum
target ECAP characteristic value and a minimum target ECAP
characteristic value at a predetermined frequency to provide a
sensation to the patient that may be perceived as a wave or other
sensation that may provide therapeutic relief for the patient. The
maximum target ECAP characteristic value, the minimum target ECAP
characteristic value, and the predetermined frequency may be stored
in the storage device of IMD 110 and may be updated in response to
a signal from external programmer 150 (e.g., a user request to
change the values stored in the storage device of IMD 110). In
other examples, the target ECAP characteristic value may be
programed to steadily increase or steadily decrease to a baseline
target ECAP characteristic value over a period of time. In other
examples, external programmer 150 may program the target ECAP
characteristic value to automatically change over time according to
other predetermined functions or patterns. In other words, the
target ECAP characteristic value may be programmed to change
incrementally by a predetermined amount or predetermined
percentage, the predetermined amount or percentage being selected
according to a predetermined function (e.g., sinusoid function,
ramp function, exponential function, logarithmic function, or the
like). Increments in which the target ECAP characteristic value is
changed may be changed for every certain number of pulses or a
certain unit of time. Although the system may change the target
ECAP characteristic value, received ECAP signals may still be used
by the system to adjust one or more parameter values of the
informed pulses and/or control pulses in order to meet the target
ECAP characteristic value.
[0076] In some examples, IMD 110 includes stimulation generation
circuitry configured to deliver electrical stimulation therapy to
the patient 105, where the electrical stimulation therapy includes
a plurality of informed pulses. Additionally, the stimulation
generation circuitry of IMD 110 may be configured to deliver a
plurality of control pulses, where the plurality of control pulses
is interleaved with at least some informed pulses of the plurality
of informed pulses. In some examples, IMD 110 includes sensing
circuitry configured to detect a plurality of ECAPs, where the
sensing circuitry is configured to detect each ECAP of the
plurality of ECAPs after a control pulse of the plurality of
control pulses and prior to a subsequent therapy pulse of the
plurality of informed pulses. Even though the plurality of ECAPs
may be received by IMD 110 based on IMD 110 delivering the
plurality of control pulses (e.g., the plurality of control pulses
may evoke the plurality of ECAPs received by IMD 110), the
plurality of ECAPs may indicate an efficacy of the plurality of
informed pulses. In other words, although the plurality of ECAPs
might, in some cases, not be evoked by the plurality of informed
pulses themselves, the plurality of ECAPs may still reveal one or
more properties of the plurality of informed pulses or one or more
effects of the plurality of informed pulses on patient 105. In some
examples, the plurality of informed pulses are delivered by IMD 110
at above a perception threshold, where patient 105 is able to
perceive the plurality of informed pulses delivered at above the
perception threshold. In other examples, the plurality of informed
pulses are delivered by IMD 110 at below a perception threshold,
where the patient 105 not able to perceive the plurality of
informed pulses delivered at below the perception threshold.
[0077] IMD 110 may include processing circuitry which, in some
examples, is configured to process the plurality of ECAPs received
by the sensing circuitry of IMD 110. For example, the processing
circuitry of IMD 110 is configured to determine if a parameter of a
first ECAP is greater than a threshold parameter value. The
processing circuitry may monitor a characteristic value of each
ECAP of the plurality of ECAPs and the first ECAP may be the first
ECAP of the plurality of ECAPs recorded by IMD 110 that exceeds the
threshold characteristic value. In some examples, the
characteristic monitored by IMD 110 may be an ECAP amplitude. The
ECAP amplitude may, in some examples, be given by a voltage
difference between an N1 ECAP peak and a P2 ECAP peak. More
description related to the N1 ECAP peak, and other ECAP peaks may
be found below in the FIG. 4 description. In other examples, IMD
110 may monitor another characteristic or more than one
characteristic of the plurality of ECAPs, such as current
amplitude, slope, slew rate, ECAP frequency, ECAP duration, or any
combination thereof. In some examples where the characteristic
includes an ECAP amplitude, the threshold ECAP characteristic value
may be selected from a range of approximately 5 microvolts (.mu.V)
to approximately 30 .mu.V.
[0078] If the processing circuitry of IMD 110 determines that the
characteristic of the first ECAP is greater than the threshold ECAP
characteristic value, the processing circuitry may decrement (or
reduce) a parameter of a set of informed pulses delivered by the
stimulation generation circuitry after the first ECAP. In some
examples, in order to decrement the parameter of the set of
informed pulses, IMD 110 may decrease a current amplitude of each
therapy pulse of each consecutive therapy pulse of the set of
informed pulses by a current amplitude value. In other examples, in
order to decrement the parameter of the set of informed pulses, IMD
110 may decrease a magnitude of a parameter (e.g., voltage) other
than current. Since the plurality of ECAPs may indicate some
effects of the therapy delivered by IMD 110 on patient 105, IMD 110
may decrement the parameter of the set of informed pulses in order
to improve the therapy delivered to patient 105. In some cases,
ECAPs received by IMD 110 exceeding the threshold ECAP
characteristic value may indicate to IMD 110 that one or more of
leads 130 have moved closer to the target tissue (e.g., spinal cord
120) of patient 105. In these cases, if therapy delivered to spinal
cord 120 is maintained at present levels, patient 105 may
experience transient overstimulation since the distance between
leads 130 and the target tissue of patient 105 is a factor in
determining the effects of electrical stimulation therapy on
patient 105. Consequently, decrementing the first set of informed
pulses based on determining that the first ECAP exceeds the
threshold ECAP characteristic value may prevent patient 105 from
experiencing transient overstimulation due to the electrical
stimulation therapy delivered by IMD 110.
[0079] After determining that the first ECAP exceeds the threshold
ECAP characteristic value, the processing circuitry of IMD 110 may
continue to monitor the plurality of ECAPs detected by the sensing
circuitry. In some examples, the processing circuitry of IMD 110
may identify a second ECAP which occurs after the first ECAP, where
a characteristic of the second ECAP is less than the threshold ECAP
characteristic value. The second ECAP may, in some cases, be a
leading ECAP occurring after the first ECAP which includes a
characteristic value less than the threshold ECAP characteristic
value. In other words, each ECAP occurring between the first ECAP
and the second ECAP may include a characteristic value greater than
or equal to the threshold ECAP characteristic value. In this
manner, since IMD 110 may decrement the informed pulses delivered
to patient 105 between the first ECAP and the second ECAP,
decreasing a risk that patient 105 experiences transient
overstimulation during a period of time extending between the
reception of the first ECAP and the reception of the second ECAP.
Based on the characteristic of the second ECAP being less than the
threshold ECAP characteristic value, the processing circuitry of
IMD 110 may increment a parameter of a second set of informed
pulses delivered by the stimulation generation circuitry after the
second ECAP.
[0080] In some examples, IMD 110 may deliver electrical stimulation
therapy to patient 105 based on a "control policy." In some
examples, IMD 110 stores the control policy in a memory (not
illustrated in FIG. 1). The control policy may be set and/or
updated by processing circuitry of IMD 110 or processing circuitry
of external programmer 150, processing circuitry of one or more
other devices, or any combination thereof. The control policy
drives one or more therapy configurations of the electrical
stimulation therapy delivered by IMD 110. For example, the control
policy may determine an amplitude of one or more stimulation pulses
delivered by IMD 110, a frequency of electrical stimulation therapy
delivered by IMD 110, a response to one or more detected ECAPs
(e.g., changes in pulse amplitude and/or pulse frequency), or any
combination thereof.
[0081] External programmer 150 or another device may include a user
interface. Processing circuitry (e.g., processing circuitry of
external programmer 150 and/or processing circuitry of IMD 110) may
output, for display by the user interface, a message requesting the
patient 105 perform a set of actions. The processing circuitry may
receive, from the user interface, user input indicative of a
patient response associated with the set of actions. Additionally,
the processing circuitry may determine, based on the user input,
one or more adjustments to a control policy which controls
electrical stimulation delivered by IMD 110 based on at least one
evoked compound action potentials (ECAP) sensed by IMD 110.
[0082] In some examples, responsive to determining the one or more
adjustments to the control policy, the processing circuitry is
configured to output, to IMD 110 via communication circuitry of
external programmer 150, an instruction to configure the one or
more adjustments to the control policy, but this is not required.
The one or more adjustments may be implemented in other ways.
[0083] In some examples, to determine the one or more adjustments
to the control policy, the processing circuitry is configured to
determine the one or more adjustments in order to cause the control
policy to perform any one or combination of: decrease a decrement
step size or a decrement step rate of a plurality of stimulation
pulses delivered to IMD 110 responsive to one or more events
associated with a patient response, increase the decrement step
size or the decrement step rate of the plurality of stimulation
pulses responsive to the one or more events associated with the
patient response, decrease an increment step size or an increment
step rate of the plurality of stimulation pulses responsive to the
one or more events associated with the patient response, or
increase the increment step size or the increment step rate of the
plurality of stimulation pulses responsive to the transient one or
more events associated with the patient response. The one or more
adjustments to the control policy are not meant to be limited to
these examples. An adjustment to the control policy may cause the
control policy to make any kind of change to the therapy delivered
to patient 105 by IMD 110 or another device.
[0084] The message requesting patient 105 to perform a set of
actions and the user input indicative of the patient response
associated with an evaluation technique referred to herein as the
"patient guidance wizard" (e.g., a methodology for setting up
stimulation therapy and/or control policy for therapy using a user
interface to provide and receive information to and from a user
such as a clinician and/or patient). The patient guidance wizard
may represent a technique in which processing circuitry outputs the
message requesting patient 105 to perform an action (e.g., an arch
of the back, a cough, or another action). Subsequently, to perform
the patient guidance wizard, the processing circuitry may output a
set of requests via the user interface of external programmer 150
or another device and receive a set of responses to the set of
requests. Each request of the set of requests may include a prompt
for information relating to one or more patient sensations
corresponding to the action and each response may include
information relating to the respective request. Based on the set of
responses received from the user interface, the processing
circuitry may determine the one or more adjustments to be made to
the therapy delivered by patient 105.
[0085] In some examples, stimulation generation circuitry of IMD
110 is configured to deliver electrical stimulation to patient 105,
where the electrical stimulation therapy includes a plurality of
stimulation pulses. Additionally, IMD 110 may include sensing
circuitry configured to sense one or more evoked compound action
potentials (ECAPs), wherein the sensing circuitry is configured to
sense each ECAP of the one or more ECAPs elicited by a respective
stimulation pulse of the plurality of stimulation pulses.
Processing circuitry of IMD 110 may store histogram data
corresponding to a set of ECAPs of the plurality of ECAPs, the set
of ECAPs being sensed by the sensing circuitry of IMD 110 over a
window of time.
[0086] In some examples, the histogram data includes a set of
histograms. Each histogram of the set of histograms includes a set
of histogram bins. Each histogram bin of the set of histogram bins
corresponds to a range of ECAP parameter values, and each histogram
bin of the set of histogram bins includes a number of ECAPs of the
set of ECAPs that are associated with a parameter value within the
respective range of ECAP parameter values. The number of ECAPs in
each histogram bin may be any number greater than or equal to zero.
The set of histograms may represent a sequence of histograms, where
each histogram of the sequence of histograms corresponds to a set
of ECAPs detected by IMD 110 during a respective period of time.
For example, a set of histogram data may include a sequence of
histograms, where each histogram of the sequence of histograms
corresponds to a one second window of time. That is, a first
histogram of the sequence of histograms corresponds to a first one
second window, a second histogram of the sequence of histograms
corresponds to a second one second window directly following the
first one second window, and so on. However, the sequence of
histograms may correspond to periods of time of any length.
[0087] In some examples, processing circuitry of IMD 110 may
receive, from an external device (e.g., external programmer 150), a
user input. IMD 110 may capture, in response to receiving the user
input, histogram data from a "rolling buffer" and store the
captured histogram data in a memory. IMD 110 may additionally or
alternatively capture the histogram data from the rolling buffer in
response to detecting a pattern of interest in a set of ECAPs,
detecting a pattern in an accelerometer signal, detecting a change
in a state of an algorithm, or detecting noise in any on or more
signals of IMD 110. The set of histogram data may include data
representative of the patient response. That is, IMD 110 may store
the histogram data in a "rolling buffer" which updates as time
progresses. In some cases, IMD 110 may erase data from the end of
the rolling buffer and add data to the beginning of the rolling
buffer as time progresses. When IMD 110 receives the user input,
which may represent a request to capture histogram data from the
rolling buffer, IMD 110 may capture, or permanently save, the
histogram data currently in the rolling buffer when IMD 110
receives the user request.
[0088] In some examples, IMD 110 may permanently save histogram
data without first capturing the histogram data in the rolling
buffer. For example, IMD 110 may receive a user report of a start
of a patient activity and save a first timestamp corresponding to
the start of the patient activity. Additionally, IMD 110 may
receive a user report of an end of a patient activity and save a
second timestamp corresponding to the end of the patient activity,
where the first timestamp corresponds to one of the plurality of
second sets of histogram data and the second timestamp corresponds
to one of the plurality of second sets of histogram data. IMD 110
may analyze saved histogram data based on the timestamps.
[0089] The rolling buffer may correspond to a window of time which
extends from a first time to a second time, where the second time
represents a current time and the first time represents a point in
time before the current time, and where the second time represents
a current time or a time in the future. When IMD 110 receives the
user input to capture the histogram data in the rolling buffer, IMD
110 may capture the histogram data currently stored in the rolling
buffer and the histogram data may correspond to a period of time in
which a patient response occurs. That is, the histogram data may
include one or more indications (e.g., elevated ECAP amplitudes)
which indicate a patient response such as transient
overstimulation.
[0090] IMD 110 may receive a user request to set one or more
histogram parameters for collecting the set of histogram data. The
one or more histogram parameters may include a length of a period
of time corresponding to each histogram within the histogram data,
a range of ECAP parameters corresponding to each histogram bin, or
any other parameter associated with the histogram data. IMD 110 may
set, based on the user request, the one or more histogram
parameters, wherein the one or more histogram parameters include a
set of parameter ranges which define one or more histogram bins
included in a set of histogram bins of the histogram data.
[0091] The histogram data may include a first set of histograms
corresponding to stimulation pulse amplitude values of a set of
stimulation pulses delivered by the stimulation generation
circuitry; and a second set of histograms corresponding to ECAP
amplitude values of ECAPs sensed by the sensing circuitry
responsive to the set of stimulation pulses delivered by
stimulation generation circuitry. In this way, when evaluating the
second set of histograms which include ECAP amplitude values,
processing circuitry may evaluate the ECAP amplitude values based
on the amplitude of the stimulation pulses which evoke the
respective ECAPs.
[0092] FIG. 2 is a block diagram illustrating an example
configuration of components of IMD 200, in accordance with one or
more techniques of this disclosure. IMD 200 may be an example of
IMD 110 of FIG. 1. In the example shown in FIG. 2, IMD 200 includes
stimulation generation circuitry 202, switch circuitry 204, sensing
circuitry 206, communication circuitry 208, processing circuitry
210, storage device 212, sensor(s) 222, and power source 224.
[0093] In the example shown in FIG. 2, storage device 212 stores
therapy stimulation programs 214 and ECAP test stimulation programs
216 in separate memories within storage device 212 or separate
areas within storage device 212. Storage device 212 also stores
rolling buffer 218 and histogram data 220. Each stored therapy
stimulation program of therapy stimulation programs 214 defines
values for a set of electrical stimulation parameters (e.g., a
stimulation parameter set), such as a stimulation electrode
combination, electrode polarity, current or voltage amplitude,
pulse width, pulse rate, and pulse shape. Each stored ECAP test
stimulation programs 216 defines values for a set of electrical
stimulation parameters (e.g., a control stimulation parameter set),
such as a stimulation electrode combination, electrode polarity,
current or voltage amplitude, pulse width, pulse rate, and pulse
shape. ECAP test stimulation programs 216 may also have additional
information such as instructions regarding when to deliver control
pulses based on the pulse width and/or frequency of the informed
pulses defined in therapy stimulation programs 214. In examples in
which control pulses are provided to the patient without the need
for informed pulses, a separate ECAP test stimulation program may
not be needed. Instead, the ECAP test stimulation program for
therapy that only includes control pulses may define the same
control pulses as the corresponding therapy stimulation program for
those control pulses.
[0094] Accordingly, in some examples, stimulation generation
circuitry 202 generates electrical stimulation signals in
accordance with the electrical stimulation parameters noted above.
Other ranges of stimulation parameter values may also be useful and
may depend on the target stimulation site within patient 105. While
stimulation pulses are described, stimulation signals may be of any
form, such as continuous-time signals (e.g., sine waves) or the
like. Switch circuitry 204 may include one or more switch arrays,
one or more multiplexers, one or more switches (e.g., a switch
matrix or other collection of switches), or other electrical
circuitry configured to direct stimulation signals from stimulation
generation circuitry 202 to one or more of electrodes 232, 234, or
directed sensed signals from one or more of electrodes 232, 234 to
sensing circuitry 206. In other examples, stimulation generation
circuitry 202 and/or sensing circuitry 206 may include sensing
circuitry to direct signals to and/or from one or more of
electrodes 232, 234, which may or may not also include switch
circuitry 204.
[0095] Sensing circuitry 206 monitors signals from any combination
of electrodes 232, 234. In some examples, sensing circuitry 206
includes one or more amplifiers, filters, and analog-to-digital
converters. Sensing circuitry 206 may be used to sense
physiological signals, such as ECAPs. In some examples, sensing
circuitry 206 detects ECAPs from a particular combination of
electrodes 232, 234. In some cases, the particular combination of
electrodes for sensing ECAPs includes different electrodes than a
set of electrodes 232, 234 used to deliver stimulation pulses.
Alternatively, in other cases, the particular combination of
electrodes used for sensing ECAPs includes at least one of the same
electrodes as a set of electrodes used to deliver stimulation
pulses to patient 105. Sensing circuitry 206 may provide signals to
an analog-to-digital converter, for conversion into a digital
signal for processing, analysis, storage, or output by processing
circuitry 210.
[0096] Communication circuitry 208 supports wireless communication
between IMD 200 and an external programmer (not shown in FIG. 2) or
another computing device under the control of processing circuitry
210. Processing circuitry 210 of IMD 200 may receive, as updates to
programs, values for various stimulation parameters such as
amplitude and electrode combination, from the external programmer
via communication circuitry 208. Updates to the therapy stimulation
programs 214 and ECAP test stimulation programs 216 may be stored
within storage device 212. Communication circuitry 208 in IMD 200,
as well as telemetry circuits in other devices and systems
described herein, such as the external programmer, may accomplish
communication by radiofrequency (RF) communication techniques. In
addition, communication circuitry 208 may communicate with an
external medical device programmer (not shown in FIG. 2) via
proximal inductive interaction of IMD 200 with the external
programmer. The external programmer may be one example of external
programmer 150 of FIG. 1. Accordingly, communication circuitry 208
may send information to the external programmer on a continuous
basis, at periodic intervals, or upon request from IMD 110 or the
external programmer.
[0097] Processing circuitry 210 may include any one or more of a
microprocessor, a controller, a digital signal processor (DSP), an
application specific integrated circuit (ASIC), a
field-programmable gate array (FPGA), discrete logic circuitry, or
any other processing circuitry configured to provide the functions
attributed to processing circuitry 210 herein may be embodied as
firmware, hardware, software or any combination thereof. Processing
circuitry 210 controls stimulation generation circuitry 202 to
generate stimulation signals according to therapy stimulation
programs 214 and ECAP test stimulation programs 216 stored in
storage device 212 to apply stimulation parameter values specified
by one or more of programs, such as amplitude, pulse width, pulse
rate, and pulse shape of each of the stimulation signals.
[0098] In the example shown in FIG. 2, the set of electrodes 232
includes electrodes 232A, 232B, 232C, and 232D, and the set of
electrodes 234 includes electrodes 234A, 234B, 234C, and 234D. In
other examples, a single lead may include all eight electrodes 232
and 234 along a single axial length of the lead. Processing
circuitry 210 also controls stimulation generation circuitry 202 to
generate and apply the stimulation signals to selected combinations
of electrodes 232, 234. In some examples, stimulation generation
circuitry 202 includes a switch circuit (instead of, or in addition
to, switch circuitry 204) that may couple stimulation signals to
selected conductors within leads 230, which, in turn, deliver the
stimulation signals across selected electrodes 232, 234. Such a
switch circuit may be a switch array, switch matrix, multiplexer,
or any other type of switching circuit configured to selectively
couple stimulation energy to selected electrodes 232, 234 and to
selectively sense bioelectrical neural signals of a spinal cord of
the patient (not shown in FIG. 2) with selected electrodes 232,
234.
[0099] In other examples, however, stimulation generation circuitry
202 does not include a switch circuit and switch circuitry 204 does
not interface between stimulation generation circuitry 202 and
electrodes 232, 234. In these examples, stimulation generation
circuitry 202 includes a plurality of pairs of voltage sources,
current sources, voltage sinks, or current sinks connected to each
of electrodes 232, 234 such that each pair of electrodes has a
unique signal circuit. In other words, in these examples, each of
electrodes 232, 234 is independently controlled via its own signal
circuit (e.g., via a combination of a regulated voltage source and
sink or regulated current source and sink), as opposed to switching
signals between electrodes 232, 234.
[0100] Electrodes 232, 234 on respective leads 230 may be
constructed of a variety of different designs. For example, one or
both of leads 230 may include one or more electrodes at each
longitudinal location along the length of the lead, such as one
electrode at different perimeter locations around the perimeter of
the lead at each of the locations A, B, C, and D. In one example,
the electrodes may be electrically coupled to stimulation
generation circuitry 202, e.g., via switch circuitry 204 and/or
switching circuitry of the stimulation generation circuitry 202,
via respective wires that are straight or coiled within the housing
of the lead and run to a connector at the proximal end of the lead.
In another example, each of the electrodes of the lead may be
electrodes deposited on a thin film. The thin film may include an
electrically conductive trace for each electrode that runs the
length of the thin film to a proximal end connector. The thin film
may then be wrapped (e.g., a helical wrap) around an internal
member to form the lead 230. These and other constructions may be
used to create a lead with a complex electrode geometry.
[0101] Although sensing circuitry 206 is incorporated into a common
housing with stimulation generation circuitry 202 and processing
circuitry 210 in FIG. 2, in other examples, sensing circuitry 206
may be in a separate housing from IMD 200 and may communicate with
processing circuitry 210 via wired or wireless communication
techniques.
[0102] In some examples, one or more of electrodes 232 and 234 are
suitable for sensing the ECAPs. For instance, electrodes 232 and
234 may sense the voltage amplitude of a portion of the ECAP
signals, where the sensed voltage amplitude is a characteristic the
ECAP signal.
[0103] Storage device 212 may be configured to store information
within IMD 200 during operation. Storage device 212 may include a
computer-readable storage medium or computer-readable storage
device. In some examples, storage device 212 includes one or more
of a short-term memory or a long-term memory. Storage device 212
may include, for example, random access memory (RAM), dynamic
random access memory (DRAM), static random access memory (SRAM),
ferroelectric random access memory (FRAM), magnetic discs, optical
discs, flash memory, or forms of electrically programmable memory
(EPROM) or electrically erasable and programmable memory (EEPROM).
In some examples, storage device 212 is used to store data
indicative of instructions for execution by processing circuitry
210. As discussed above, storage device 212 is configured to store
therapy stimulation programs 214 and ECAP test stimulation programs
216.
[0104] In some examples, stimulation generation circuitry 202 may
be configured to deliver electrical stimulation therapy to patient
105. The electrical stimulation therapy may, in some cases, include
a plurality of informed pulses. Additionally, stimulation
generation circuitry 202 may be configured to deliver a plurality
of control pulses, where the plurality of control pulses is
interleaved with at least some informed pulses of the plurality of
informed pulses. Stimulation generation circuitry may deliver the
plurality of informed pulses and the plurality of control pulses to
target tissue (e.g., spinal cord 120) of patient 105 via electrodes
232, 234 of leads 230. By delivering such informed pulses and
control pulses, stimulation generation circuitry 202 may evoke
responsive ECAPs in the target tissue, the responsive ECAPs
propagating through the target tissue before arriving back at
electrodes 232, 234. In some examples, a different combination of
electrodes 232, 234 may sense responsive ECAPs than a combination
of electrodes 232, 234 that delivers informed pulses and a
combination of electrodes 232, 234 that delivers control pulses.
Sensing circuitry 206 may be configured to detect the responsive
ECAPs via electrodes 232, 234 and leads 230. In other examples,
stimulation generation circuitry 202 may be configured to deliver a
plurality of control pulses, without any informed pulses, when
control pulses also provide therapeutic effect for the patient.
[0105] Processing circuitry 210 may, in some cases, direct sensing
circuitry 206 to continuously monitor for ECAPs. In other cases,
processing circuitry 210 may direct sensing circuitry 206 to may
monitor for ECAPs based on signals from sensor(s) 222. For example,
processing circuitry 210 may activate sensing circuitry 206 based
on an activity level of patient 105 exceeding an activity level
threshold (e.g., an accelerometer signal of sensor(s) 222 rises
above a threshold). Activating and deactivating sensing circuitry
206 may, in some examples, extend a battery life of power source
224.
[0106] In some examples, processing circuitry 210 determines if a
characteristic of a first ECAP is greater than a threshold ECAP
characteristic value. The threshold ECAP characteristic value may
be stored in storage device 212. In some examples, the
characteristic of the first ECAP is a voltage amplitude of the
first ECAP. In some such examples, the threshold ECAP
characteristic value is selected from a range of approximately 10
microvolts (Or) to approximately 20 .mu.V. In other examples,
processing circuitry 210 determines if another characteristic
(e.g., ECAP current amplitude, ECAP slew rate, area underneath the
ECAP, ECAP slope, or ECAP duration) of the first ECAP is greater
than the threshold ECAP characteristic value.
[0107] If processing circuitry 210 determines that the
characteristic of the first ECAP is greater than the threshold ECAP
characteristic value, processing circuitry 210 is configured to
activate a decrement mode, altering at least one parameter of each
therapy pulse of a set of informed pulses delivered by IMD 200
after the first ECAP is sensed by sensing circuitry 206.
Additionally, while the decrement mode is activated, processing
circuitry 210 may change at least one parameter of each control
pulse of a set of control pulses delivered by IMD 200 after the
first ECAP is sensed by sensing circuitry 206. In some examples,
the at least one parameter of the informed pulses and the at least
one parameter of the control pulses adjusted by processing
circuitry 210 during the decrement mode includes a stimulation
current amplitude. In some such examples, during the decrement
mode, processing circuitry 210 decreases an electrical current
amplitude of each consecutive stimulation pulse (e.g., each therapy
pulse and each control pulse) delivered by IMD 200. In other
examples, the at least one parameter of the stimulation pulses
adjusted by processing circuitry 210 during the decrement mode
include any combination of electrical current amplitude, electrical
voltage amplitude, slew rate, pulse shape, pulse frequency, or
pulse duration.
[0108] In the example illustrated by FIG. 2, the decrement mode is
stored in storage device 212 as a part of control policy 213. The
decrement mode may include a list of instructions which enable
processing circuitry 210 to adjust parameters of stimulation pulses
according to a function. In some examples, when the decrement mode
is activated, processing circuitry 210 decreases a parameter (e.g.,
an electrical current) of each consecutive therapy pulse and each
consecutive control pulse according to a linear function. In other
examples, when the decrement mode is activated, processing
circuitry 210 decreases a parameter (e.g., an electrical current)
of each consecutive therapy pulse and each consecutive control
pulse according to an exponential function, a logarithmic function,
or a piecewise function. While the decrement mode is activated,
sensing circuitry 206 may continue to monitor responsive ECAPs. In
turn, sensing circuitry 206 may detect ECAPs responsive to control
pulses delivered by IMD 200.
[0109] Throughout the decrement mode, processing circuitry may
monitor ECAPs responsive to stimulation pulses. Processing
circuitry 210 may determine if a characteristic of a second ECAP is
less than the threshold ECAP characteristic value. The second ECAP
may, in some cases, be the leading ECAP occurring after the first
ECAP which is less than the threshold ECAP characteristic value. In
other words, each ECAP recorded by sensing circuitry 206 between
the first ECAP and the second ECAP is greater than or equal to the
threshold ECAP characteristic value. Based on the characteristic of
the second ECAP being less than the threshold ECAP characteristic
value, processing circuitry 210 may deactivate the decrement mode
and activate an increment mode, thus altering at least one
parameter of each therapy pulse of a set of informed pulses
delivered by IMD 200 after the second ECAP is sensed by sensing
circuitry 206. Additionally, while the increment mode is activated,
processing circuitry 210 may change at least one parameter of each
control pulse of a set of control pulses delivered by IMD 200 after
the second ECAP is sensed by sensing circuitry 206.
[0110] In some examples, the at least one parameter of the informed
pulses and the at least one parameter of the control pulses
adjusted by processing circuitry 210 during the increment mode
includes a stimulation current amplitude. In some such examples,
during the increment mode, processing circuitry 210 increases an
electrical current amplitude of each consecutive stimulation pulse
(e.g., each therapy pulse and each control pulse) delivered by IMD
200. In other examples, the at least one parameter of the
stimulation pulses adjusted by processing circuitry 210 during the
increment mode include any combination of electrical current
amplitude, electrical voltage amplitude, slew rate, pulse shape,
pulse frequency, or pulse duration.
[0111] In the example illustrated by FIG. 2, the increment mode is
stored in storage device 212 as a part of control policy 213. The
increment mode may include a list of instructions which enable
processing circuitry 210 to adjust parameters of stimulation pulses
according to a function. In some examples, when the increment mode
is activated, processing circuitry 210 increases a parameter (e.g.,
an electrical current) of each consecutive therapy pulse and each
consecutive control pulse according to a linear function. In other
examples, when the increment mode is activated, processing
circuitry 210 increases a parameter (e.g., an electrical current)
of each consecutive therapy pulse and each consecutive control
pulse according to a non-linear function, such as an exponential
function, a logarithmic function, or a piecewise function. While
the increment mode is activated, sensing circuitry 206 may continue
to monitor responsive ECAPs. In turn, sensing circuitry 206 may
detect ECAPs responsive to control pulses delivered by IMD 200.
[0112] Processing circuitry 210 may complete the increment mode
such that the one or more parameters of the stimulation pulses
return to baseline parameter values of stimulation pulses delivered
before processing circuitry 210 activates the decrement mode (e.g.,
before sensing circuitry 206 detects the first ECAP). By first
decrementing and subsequently incrementing stimulation pulses in
response to ECAPs exceeding a threshold ECAP characteristic value,
processing circuitry 210 may prevent patient 105 from experiencing
transient overstimulation or decrease a severity of transient
overstimulation experienced by patient 105.
[0113] Although, in some examples, sensing circuitry 206 senses
ECAPs which occur in response to control pulses delivered according
to ECAP test stimulation programs 216, in other examples, sensing
circuitry 206 senses ECAPs which occur in response to informed
pulses delivered according to therapy stimulation programs 214. The
techniques of this disclosure may enable IMD 200 to toggle the
decrement mode and the increment mode using any combination of
ECAPs corresponding to informed pulses and ECAPs corresponding to
control pulses.
[0114] Sensor(s) 222 may include one or more sensing elements that
sense values of a respective patient parameter. As described,
electrodes 232 and 234 may be the electrodes that sense the
characteristic value of the ECAP. Sensor(s) 222 may include one or
more accelerometers, optical sensors, chemical sensors, temperature
sensors, pressure sensors, or any other types of sensors. Sensor(s)
222 may output patient parameter values that may be used as
feedback to control delivery of therapy. For example, sensor(s) 222
may indicate patient activity, and processing circuitry 210 may
increase the frequency of control pulses and ECAP sensing in
response to detecting increased patient activity. In one example,
processing circuitry 210 may initiate control pulses and
corresponding ECAP sensing in response to a signal from sensor(s)
222 indicating that patient activity has exceeded an activity
threshold. Conversely, processing circuitry 210 may decrease the
frequency of control pulses and ECAP sensing in response to
detecting decreased patient activity. For example, in response to
sensor(s) 222 no longer indicating that the sensed patient activity
exceeds a threshold, processing circuitry 210 may suspend or stop
delivery of control pulses and ECAP sensing. In this manner,
processing circuitry 210 may dynamically deliver control pulses and
sense ECAP signals based on patient activity to reduce power
consumption of the system when the electrode-to-neuron distance is
not likely to change and increase system response to ECAP changes
when electrode-to-neuron distance is likely to change. IMD 200 may
include additional sensors within the housing of IMD 200 and/or
coupled via one of leads 130 or other leads. In addition, IMD 200
may receive sensor signals wirelessly from remote sensors via
communication circuitry 208, for example. In some examples, one or
more of these remote sensors may be external to patient (e.g.,
carried on the external surface of the skin, attached to clothing,
or otherwise positioned external to patient 105). In some examples,
signals from sensor(s) 222 indicate a position or body state (e.g.,
sleeping, awake, sitting, standing, or the like), and processing
circuitry 210 may select target ECAP characteristic values
according to the indicated position or body state.
[0115] Power source 224 is configured to deliver operating power to
the components of IMD 200. Power source 224 may include a battery
and a power generation circuit to produce the operating power. In
some examples, the battery is rechargeable to allow extended
operation. In some examples, recharging is accomplished through
proximal inductive interaction between an external charger and an
inductive charging coil within IMD 200. Power source 224 may
include any one or more of a plurality of different battery types,
such as nickel cadmium batteries and lithium ion batteries.
[0116] FIG. 3 is a block diagram illustrating an example
configuration of components of external programmer 300, in
accordance with one or more techniques of this disclosure. External
programmer 300 may be an example of external programmer 150 of FIG.
1. Although external programmer 300 may generally be described as a
hand-held device, external programmer 300 may be a larger portable
device or a more stationary device. In addition, in other examples,
external programmer 300 may be included as part of an external
charging device or include the functionality of an external
charging device. As illustrated in FIG. 3, external programmer 300
may include processing circuitry 352, storage device 354, user
interface 356, communication circuitry 358, and power source 360.
Storage device 354 may store instructions that, when executed by
processing circuitry 352, cause processing circuitry 352 and
external programmer 300 to provide the functionality ascribed to
external programmer 300 throughout this disclosure. Each of these
components, circuitry, or modules, may include electrical circuitry
that is configured to perform some, or all of the functionality
described herein. For example, processing circuitry 352 may include
processing circuitry configured to perform the processes discussed
with respect to processing circuitry 352.
[0117] In general, external programmer 300 includes any suitable
arrangement of hardware, alone or in combination with software
and/or firmware, to perform the techniques attributed to external
programmer 300, and processing circuitry 352, user interface 356,
and communication circuitry 358 of external programmer 300. In
various examples, external programmer 300 may include one or more
processors, such as one or more microprocessors, DSPs, ASICs,
FPGAs, or any other equivalent integrated or discrete logic
circuitry, as well as any combinations of such components. External
programmer 300 also, in various examples, may include a storage
device 354, such as RAM, ROM, PROM, EPROM, EEPROM, flash memory, a
hard disk, a CD-ROM, including executable instructions for causing
the one or more processors to perform the actions attributed to
them. Moreover, although processing circuitry 352 and communication
circuitry 358 are described as separate modules, in some examples,
processing circuitry 352 and communication circuitry 358 are
functionally integrated. In some examples, processing circuitry 352
and communication circuitry 358 correspond to individual hardware
units, such as ASICs, DSPs, FPGAs, or other hardware units.
[0118] Storage device 354 (e.g., a storage device) may store
instructions that, when executed by processing circuitry 352, cause
processing circuitry 352 and external programmer 300 to provide the
functionality ascribed to external programmer 300 throughout this
disclosure. For example, storage device 354 may include
instructions that cause processing circuitry 352 to obtain a
parameter set from memory, select a spatial electrode movement
pattern, or receive a user input and send a corresponding command
to IMD 200, or instructions for any other functionality. In
addition, storage device 354 may include a plurality of programs,
where each program includes a parameter set that defines
stimulation pulses, such as control pulses and/or informed pulses.
Storage device 354 may also store data received from a medical
device (e.g., IMD 110). For example, storage device 354 may store
ECAP related data recorded at a sensing module of the medical
device, and storage device 354 may also store data from one or more
sensors of the medical device.
[0119] User interface 356 may include a button or keypad, lights, a
speaker for voice commands, a display, such as a liquid crystal
(LCD), light-emitting diode (LED), or organic light-emitting diode
(OLED). In some examples the display includes a touch screen. User
interface 356 may be configured to display any information related
to the delivery of electrical stimulation, identified patient
behaviors, sensed patient parameter values, patient behavior
criteria, or any other such information. User interface 356 may
also receive user input via user interface 356. The input may be,
for example, in the form of pressing a button on a keypad or
selecting an icon from a touch screen. The input may request
starting or stopping electrical stimulation, the input may request
a new spatial electrode movement pattern or a change to an existing
spatial electrode movement pattern, of the input may request some
other change to the delivery of electrical stimulation. In some
examples, user interface 356 may display one or more requests of
the patient guidance wizard performed by the system including
external programmer 300 and/or IMD 110, and user interface 356 may
receive one or more user responses to the one or more requests.
[0120] Communication circuitry 358 may support wireless
communication between the medical device and external programmer
300 under the control of processing circuitry 352. Communication
circuitry 358 may also be configured to communicate with another
computing device via wireless communication techniques, or direct
communication through a wired connection. In some examples,
communication circuitry 358 provides wireless communication via an
RF or proximal inductive medium. In some examples, communication
circuitry 358 includes an antenna, which may take on a variety of
forms, such as an internal or external antenna.
[0121] Examples of local wireless communication techniques that may
be employed to facilitate communication between external programmer
300 and IMD 110 include RF communication according to the 802.11 or
Bluetooth.RTM. specification sets or other standard or proprietary
telemetry protocols. In this manner, other external devices may be
capable of communicating with external programmer 300 without
needing to establish a secure wireless connection. As described
herein, communication circuitry 358 may be configured to transmit a
spatial electrode movement pattern or other stimulation parameter
values to IMD 110 for delivery of electrical stimulation
therapy.
[0122] In some examples, selection of stimulation parameters or
therapy stimulation programs are transmitted to the medical device
for delivery to a patient (e.g., patient 105 of FIG. 1). In other
examples, the therapy may include medication, activities, or other
instructions that patient 105 must perform themselves or a
caregiver perform for patient 105. In some examples, external
programmer 300 provides visual, audible, and/or tactile
notifications that indicate there are new instructions. External
programmer 300 requires receiving user input acknowledging that the
instructions have been completed in some examples.
[0123] According to the techniques of the disclosure, user
interface 356 of external programmer 300 receives an indication
from a clinician instructing a processor of the medical device to
update one or more therapy stimulation programs or to update one or
more ECAP test stimulation programs. Updating therapy stimulation
programs and ECAP test stimulation programs may include changing
one or more parameters of the stimulation pulses delivered by the
medical device according to the programs, such as amplitude, pulse
width, frequency, and pulse shape of the informed pulses and/or
control pulses. User interface 356 may also receive instructions
from the clinician commanding any electrical stimulation, including
control pulses and/or informed pulses to commence or to cease.
[0124] Power source 360 is configured to deliver operating power to
the components of external programmer 300. Power source 360 may
include a battery and a power generation circuit to produce the
operating power. In some examples, the battery is rechargeable to
allow extended operation. Recharging may be accomplished by
electrically coupling power source 360 to a cradle or plug that is
connected to an alternating current (AC) outlet. In addition,
recharging may be accomplished through proximal inductive
interaction between an external charger and an inductive charging
coil within external programmer 300. In other examples, traditional
batteries (e.g., nickel cadmium or lithium ion batteries) may be
used. In addition, external programmer 300 may be directly coupled
to an alternating current outlet to operate.
[0125] The architecture of external programmer 300 illustrated in
FIG. 3 is shown as an example. The techniques as set forth in this
disclosure may be implemented in the example external programmer
300 of FIG. 3, as well as other types of systems not described
specifically herein. Nothing in this disclosure should be construed
so as to limit the techniques of this disclosure to the example
architecture illustrated by FIG. 3.
[0126] FIG. 4 is a graph 402 of example evoked compound action
potentials (ECAPs) sensed for respective stimulation pulses, in
accordance with one or more techniques of this disclosure. As shown
in FIG. 4, graph 402 shows example ECAP signal 404 (dotted line)
and ECAP signal 406 (solid line). In some examples, each of ECAP
signals 404 and 406 are sensed from control pulses that were
delivered from a guarded cathode, where the control pulses are
bi-phasic pulses including an interphase interval between each
positive and negative phase of the pulse. In some such examples,
the guarded cathode includes stimulation electrodes located at the
end of an 8-electrode lead (e.g., leads 130 of FIG. 1) while two
sensing electrodes are provided at the other end of the 8-electrode
lead. ECAP signal 404 illustrates the voltage amplitude sensed as a
result from a sub-detection threshold stimulation pulse, or a
stimulation pulse which results in no detectable ECAP. Peaks 408 of
ECAP signal 404 are detected and represent the artifact of the
delivered control pulse. However, no propagating signal is detected
after the artifact in ECAP signal 404 because the control pulse was
sub-detection stimulation threshold.
[0127] In contrast to ECAP signal 404, ECAP signal 406 represents
the voltage amplitude detected from a supra-detection stimulation
threshold control pulse. Peaks 408 of ECAP signal 406 are detected
and represent the artifact of the delivered control pulse. After
peaks 408, ECAP signal 406 also includes peaks P1, N1, and P2,
which are three typical peaks representative of propagating action
potentials from an ECAP. The example duration of the artifact and
peaks P1, N1, and P2 is approximately 1 millisecond (ms). When
detecting the ECAP of ECAP signal 406, different characteristics
may be identified. For example, the characteristic of the ECAP may
be the amplitude between N1 and P2. This N1-P2 amplitude may be
easily detectable even if the artifact impinges on P1, a relatively
large signal, and the N1-P2 amplitude may be minimally affected by
electronic drift in the signal. In other examples, the
characteristic of the ECAP used to control subsequent control
pulses and/or informed pulses may be an amplitude of P1, N1, or P2
with respect to neutral or zero voltage. In some examples, the
characteristic of the ECAP used to control subsequent control
pulses or informed pulses is a sum of two or more of peaks P1, N1,
or P2. In other examples, the characteristic of ECAP signal 406 may
be the area under one or more of peaks P1, N1, and/or P2. In other
examples, the characteristic of the ECAP may be a ratio of one of
peaks P1, N1, or P2 to another one of the peaks. In some examples,
the characteristic of the ECAP is a slope between two points in the
ECAP signal, such as the slope between N1 and P2. In other
examples, the characteristic of the ECAP may be the time between
two points of the ECAP, such as the time between N1 and P2. The
time between when the stimulation pulse is delivered and a point in
the ECAP signal may be referred to as a latency of the ECAP and may
indicate the types of fibers being captured by the stimulation
pulse (e.g., a control pulse). ECAP signals with lower latency
(i.e., smaller latency values) indicate a higher percentage of
nerve fibers that have faster propagation of signals, whereas ECAP
signals with higher latency (i.e., larger latency values) indicate
a higher percentage of nerve fibers that have slower propagation of
signals. Latency may also refer to the time between an electrical
feature is detected at one electrode and then detected again at a
different electrode. This time, or latency, is inversely
proportional to the conduction velocity of the nerve fibers. Other
characteristics of the ECAP signal may be used in other
examples.
[0128] The amplitude of the ECAP signal increases with increased
amplitude of the control pulse, as long as the pulse amplitude is
greater than threshold such that nerves depolarize and propagate
the signal. The target ECAP characteristic (e.g., the target ECAP
amplitude) may be determined from the ECAP signal detected from a
control pulse when informed pulses are determined to deliver
effective therapy to patient 105. The ECAP signal thus is
representative of the distance between the stimulation electrodes
and the nerves appropriate for the stimulation parameter values of
the informed pulses delivered at that time. Therefore, IMD 110 may
attempt to use detected changes to the measured ECAP characteristic
value to change therapy pulse parameter values and maintain the
target ECAP characteristic value during therapy pulse delivery.
[0129] FIG. 5A is a timing diagram 500A illustrating an example of
electrical stimulation pulses, respective stimulation signals, and
respective sensed ECAPs, in accordance with one or more techniques
of this disclosure. For convenience, FIG. 5A is described with
reference to IMD 200 of FIG. 2. As illustrated, timing diagram 500A
includes first channel 502, a plurality of stimulation pulses
504A-504N (collectively "stimulation pulses 504"), second channel
506, a plurality of respective ECAPs 508A-508N (collectively "ECAPs
508"), and a plurality of stimulation signals 509A-509N
(collectively "stimulation signals 509"). In some examples,
stimulation pulses 504 may represent control pulses which are
configured to elicit ECAPs 508 that are detectible by IMD 200, but
this is not required. Stimulation pulses 504 may represent any type
of pulse that is deliverable by IMD 200. In the example of FIG. 5A,
IMD 200 can deliver therapy with control pulses instead of, or
without, informed pulses.
[0130] First channel 502 is a time/voltage (and/or current) graph
indicating the voltage (or current) of at least one electrode of
electrodes 232, 234. In one example, the stimulation electrodes of
first channel 502 may be located on the opposite side of the lead
as the sensing electrodes of second channel 506. Stimulation pulses
504 may be electrical pulses delivered to the spinal cord of the
patient by at least one of electrodes 232, 234, and stimulation
pulses 504 may be balanced biphasic square pulses with an
interphase interval. In other words, each of stimulation pulses 504
are shown with a negative phase and a positive phase separated by
an interphase interval. For example, a stimulation pulse 504 may
have a negative voltage for the same amount of time and amplitude
that it has a positive voltage. It is noted that the negative
voltage phase may be before or after the positive voltage phase.
Stimulation pulses 504 may be delivered according to test
stimulation programs 216 stored in storage device 212 of IMD 200,
and test stimulation programs 216 may be updated according to user
input via an external programmer and/or may be updated according to
a signal from sensor(s) 222. In one example, stimulation pulses 504
may have a pulse width of less than approximately 300 microseconds
(e.g., the total time of the positive phase, the negative phase,
and the interphase interval is less than 300 microseconds). In
another example, stimulation pulses 504 may have a pulse width of
approximately 100 .mu.s for each phase of the bi-phasic pulse. As
illustrated in FIG. 5A, stimulation pulses 504 may be delivered via
channel 502. Delivery of stimulation pulses 504 may be delivered by
leads 230 in a guarded cathode electrode combination. For example,
if leads 230 are linear 8-electrode leads, a guarded cathode
combination is a central cathodic electrode with anodic electrodes
immediately adjacent to the cathodic electrode.
[0131] Second channel 506 is a time/voltage (and/or current) graph
indicating the voltage (or current) of at least one electrode of
electrodes 232, 234. In one example, the electrodes of second
channel 506 may be located on the opposite side of the lead as the
electrodes of first channel 502. ECAPs 508 may be sensed at
electrodes 232, 234 from the spinal cord of the patient in response
to stimulation pulses 504. ECAPs 508 are electrical signals which
may propagate along a nerve away from the origination of
stimulation pulses 504. In one example, ECAPs 508 are sensed by
different electrodes than the electrodes used to deliver
stimulation pulses 504. As illustrated in FIG. 5A, ECAPs 508 may be
recorded on second channel 506.
[0132] Stimulation signals 509A, 509B, and 509N may be sensed by
leads 230 and sensing circuitry 206 and may be sensed during the
same period of time as the delivery of stimulation pulses 504.
Since the stimulation signals may have a greater amplitude and
intensity than ECAPs 508, any ECAPs arriving at IMD 200 during the
occurrence of stimulation signals 509 might not be adequately
sensed by sensing circuitry 206 of IMD 200. However, ECAPs 508 may
be sufficiently sensed by sensing circuitry 206 because each ECAP
508, or at least a portion of ECAP 508 used as feedback for
stimulation pulses 504, falls after the completion of each a
stimulation pulse 504. As illustrated in FIG. 5A, stimulation
signals 509 and ECAPs 508 may be recorded on channel 506. In some
examples, ECAPs 508 may not follow respective stimulation signals
509 when ECAPs are not elicited by stimulation pulses 504 or the
amplitude of ECAPs is too low to be detected (e.g., below the
detection threshold).
[0133] FIG. 5B is a timing diagram 500B illustrating one example of
electrical stimulation pulses, respective stimulation signals, and
respective sensed ECAPs, in accordance with one or more techniques
of this disclosure. For convenience, FIG. 5B is described with
reference to IMD 200 of FIG. 2. As illustrated, timing diagram 500B
includes first channel 510, a plurality of control pulses 512A-512N
(collectively "control pulses 512"), second channel 520, a
plurality of informed pulses 524A-524N (collectively "informed
pulses 524") including passive recharge phases 526A-526N
(collectively "passive recharge phases 526"), third channel 530, a
plurality of respective ECAPs 536A-536N (collectively "ECAPs 536"),
and a plurality of stimulation signals 538A-538N (collectively
"stimulation signals 538").
[0134] First channel 510 is a time/voltage (and/or current) graph
indicating the voltage (or current) of at least one electrode of
electrodes 232, 234. In one example, the stimulation electrodes of
first channel 510 may be located on the opposite side of the lead
as the sensing electrodes of third channel 530. Control pulses 512
may be electrical pulses delivered to the spinal cord of the
patient by at least one of electrodes 232, 234, and control pulses
512 may be balanced biphasic square pulses with an interphase
interval. In other words, each of control pulses 512 are shown with
a negative phase and a positive phase separated by an interphase
interval. For example, a control pulse 512 may have a negative
voltage for the same amount of time that it has a positive voltage.
It is noted that the negative voltage phase may be before or after
the positive voltage phase. Control pulses 512 may be delivered
according to test stimulation programs 216 stored in storage device
212 of IMD 200, and test stimulation programs 216 may be updated
according to user input via an external programmer and/or may be
updated according to a signal from sensor(s) 222. In one example,
control pulses 512 may have a pulse width of 300 microseconds
(e.g., the total time of the positive phase, the negative phase,
and the interphase interval is 300 microseconds). In another
example, control pulses 512 may have a pulse width of approximately
100 .mu.s for each phase of the bi-phasic pulse. As illustrated in
FIG. 5B, control pulses 512 may be delivered via first channel 510.
Delivery of control pulses 512 may be delivered by leads 230 in a
guarded cathode electrode combination. For example, if leads 230
are linear 8-electrode leads, a guarded cathode combination is a
central cathodic electrode with anodic electrodes immediately
adjacent to the cathodic electrode.
[0135] Second channel 520 is a time/voltage (and/or current) graph
indicating the voltage (or current) of at least one electrode of
electrodes 232, 234 for the informed pulses. In one example, the
electrodes of second channel 520 may partially or fully share
common electrodes with the electrodes of first channel 510 and
third channel 530. Informed pulses 524 may also be delivered by the
same leads 230 that are configured to deliver control pulses 512.
Informed pulses 524 may be interleaved with control pulses 512,
such that the two types of pulses are not delivered during
overlapping periods of time. However, informed pulses 524 may or
may not be delivered by exactly the same electrodes that deliver
control pulses 512. Informed pulses 524 may be monophasic pulses
with pulse widths of greater than approximately 300 .mu.s and less
than approximately 1000 .mu.s. In fact, informed pulses 524 may be
configured to have longer pulse widths than control pulses 512. As
illustrated in FIG. 5B, informed pulses 524 may be delivered on
second channel 520.
[0136] Informed pulses 524 may be configured for passive recharge.
For example, each informed pulse 524 may be followed by a passive
recharge phase 526 to equalize charge on the stimulation
electrodes. Unlike a pulse configured for active recharge, where
remaining charge on the tissue following a stimulation pulse is
instantly removed from the tissue by an opposite applied charge,
passive recharge allows tissue to naturally discharge to some
reference voltage (e.g., ground or a rail voltage) following the
termination of the therapy pulse. In some examples, the electrodes
of the medical device may be grounded at the medical device body.
In this case, following the termination of informed pulse 524, the
charge on the tissue surrounding the electrodes may dissipate to
the medical device, creating a rapid decay of the remaining charge
at the tissue following the termination of the pulse. This rapid
decay is illustrated in passive recharge phases 526. Passive
recharge phase 526 may have a duration in addition to the pulse
width of the preceding informed pulse 524. In other examples (not
pictured in FIG. 5B), informed pulses 524 may be bi-phasic pulses
having a positive and negative phase (and, in some examples, an
interphase interval between each phase) which may be referred to as
pulses including active recharge. An informed pulse that is a
bi-phasic pulse may or may not have a following passive recharge
phase.
[0137] Third channel 530 is a time/voltage (and/or current) graph
indicating the voltage (or current) of at least one electrode of
electrodes 232, 234. In one example, the electrodes of third
channel 530 may be located on the opposite side of the lead as the
electrodes of first channel 510. ECAPs 536 may be sensed at
electrodes 232, 234 from the spinal cord of the patient in response
to control pulses 512. ECAPs 536 are electrical signals which may
propagate along a nerve away from the origination of control pulses
512. In one example, ECAPs 536 are sensed by different electrodes
than the electrodes used to deliver control pulses 512. As
illustrated in FIG. 5B, ECAPs 536 may be recorded on third channel
530.
[0138] Stimulation signals 538A, 538B, and 538N may be sensed by
leads 230 and may be sensed during the same period of time as the
delivery of control pulses 512 and informed pulses 524. Since the
stimulation signals may have a greater amplitude and intensity than
ECAPs 536, any ECAPs arriving at IMD 200 during the occurrence of
stimulation signals 538 may not be adequately sensed by sensing
circuitry 206 of IMD 200. However, ECAPs 536 may be sufficiently
sensed by sensing circuitry 206 because each ECAP 536 falls after
the completion of each a control pulse 512 and before the delivery
of the next informed pulse 524. As illustrated in FIG. 5B,
stimulation signals 538 and ECAPs 536 may be recorded on channel
530.
[0139] FIG. 6A is a timing diagram 600A illustrating an example of
electrical stimulation pulses, respective stimulation signals, and
respective sensed ECAPs, in accordance with one or more techniques
of this disclosure. For convenience, FIG. 6A is described with
reference to IMD 200 of FIG. 2. As illustrated, timing diagram 600A
includes first channel 602, a plurality of stimulation pulses
604A-604N (collectively "stimulation pulses 604"), second channel
606, a plurality of respective ECAPs 608A-608N (collectively "ECAPs
608"), and a plurality of stimulation signals 609A-609N
(collectively "stimulation signals 609"). In some examples,
stimulation pulses 604 may represent control pulses which are
configured to elicit ECAPs 608 that are detectible by IMD 200, but
this is not required. Stimulation pulses 604 may represent any type
of pulse that is deliverable by IMD 200. In the example of FIG. 6A,
IMD 200 can deliver therapy with control pulses instead of, or
without, informed pulses.
[0140] Timing diagram 600A of FIG. 6A may be substantially the same
as timing diagram 500A FIG. 5A except that stimulation pulse 604A
and stimulation pulse 604N do not evoke an ECAP that is detectible
by IMD 200. Although stimulation pulse 604B emits ECAP 608B, which
is detectible by IMD 200, it may be the case that IMD 200 does not
sense enough detectible ECAPs for therapy determination in the
example of FIG. 6A. As such, IMD 200 may determine one or more
characteristics of stimulation signals 609 in order to determine
one or more parameters of upcoming stimulation pulses following
stimulation pulse 604N. For example, IMD 200 may determine an
amplitude of at least a portion of each stimulation signal of
stimulation signals 609 and determine the one or more parameters of
the upcoming stimulation pulses based on the determined amplitudes.
Although stimulation signals 609 are illustrated as square pulses,
stimulation signals 609 may include other shapes and/or waveforms,
in some examples. In some examples, each stimulation signal of
stimulation signals 509 may include two or more phases. Processing
circuitry 210 of IMD 200 may analyze the two or more phases of
stimulation signals 509 in order to determine therapy.
[0141] FIG. 6B is a timing diagram 600B illustrating another
example of electrical stimulation pulses, respective stimulation
signals, and respective sensed ECAPs, in accordance with one or
more techniques of this disclosure. For convenience, FIG. 6B is
described with reference to IMD 200 of FIG. 2. As illustrated,
timing diagram 600B includes first channel 610, a plurality of
control pulses 612A-612N (collectively "control pulses 612"),
second channel 620, a plurality of informed pulses 624A-624N
(collectively "informed pulses 624") including passive recharge
phases 626A-626N (collectively "passive recharge phases 626"),
third channel 630, a plurality of respective ECAPs 636A-636N
(collectively "ECAPs 636"), and a plurality of stimulation signals
638A-638N (collectively "stimulation signals 638").
[0142] Timing diagram 600B of FIG. 6B may be substantially the same
as timing diagram 500B FIG. 5B except that control pulse 612A and
control pulse 612N do not evoke an ECAP that is detectible by IMD
200. Although control pulse 612B emits ECAP 636B, which is
detectible by IMD 200, it may be the case that IMD 200 does not
sense enough detectible ECAPs for therapy determination in the
example of FIG. 6B. As such, IMD 200 may determine one or more
characteristics of stimulation signals 638 in order to determine
one or more parameters of upcoming stimulation pulses following
control pulse 612N. For example, IMD 200 may determine an amplitude
of at least a portion of each stimulation signal of stimulation
signals 638 and determine the one or more parameters of the
upcoming stimulation pulses based on the determined amplitudes.
Although stimulation signals 638 are illustrated as square pulses,
stimulation signals 639 may include other shapes and/or waveforms,
in some examples. In some examples, each stimulation signal of
stimulation signals 638 may include two or more phases. Processing
circuitry 210 of IMD 200 may analyze the two or more phases of
stimulation signals 638 in order to determine therapy.
[0143] FIG. 7 is a timing diagram 700 illustrating another example
of electrical stimulation pulses, respective stimulation signals,
and respective ECAPs, in accordance with one or more techniques of
this disclosure. For convenience, FIG. 7 is described with
reference to IMD 200 of FIG. 2. As illustrated, timing diagram 700
includes first channel 710, a plurality of control pulses 712A-712N
(collectively "control pulses 712"), second channel 720, a
plurality of informed pulses 724A-724B (collectively "informed
pulses 724") including passive recharge phases 726A-726B
(collectively "passive recharge phases 726"), third channel 730, a
plurality of respective ECAPs 736A-736N (collectively "ECAPs 736"),
and a plurality of stimulation interference signals 738A-738N
(collectively "stimulation interference signals 738"). FIG. 7 may
be substantially similar to FIG. 5B, except for the differences
detailed below.
[0144] Two or more (e.g. two) control pulses 712 may be delivered
during each time event (e.g., window) of a plurality of time
events, and each time event represents a time between two
consecutive informed pulses 724. For example, during each time
event, a first control pulse may be directly followed by a first
respective ECAP, and subsequent to the completion of the first
respective ECAP, a second control pulse may be directly followed by
a second respective ECAP. Informed pulses may commence following
the second respective ECAP. In other examples not illustrated here,
three or more control pulses 712 may be delivered, and respective
ECAP signals sensed, during each time event of the plurality of
time events.
[0145] FIG. 8 is a timing diagram 800 illustrating another example
of electrical stimulation pulses, respective stimulation signals,
and respective ECAPs, in accordance with one or more techniques of
this disclosure. For convenience, FIG. 8 is described with
reference to IMD 200 of FIG. 2. As illustrated, timing diagram 800
includes first channel 810, a plurality of control pulses 812A-812N
(collectively "control pulses 812"), second channel 820, a
plurality of informed pulses 824A-824B (collectively "informed
pulses 824") including passive recharge phases 826A-826B
(collectively "passive recharge phases 826"), third channel 830,
respective ECAPs 836B (collectively "ECAPs 836"), and a plurality
of stimulation interference signals 838A-838N (collectively
"stimulation interference signals 838"). Timing diagram 800 of FIG.
8 may be substantially the same as timing diagram 700 FIG. 7 except
that control pulses 812A and control pulses 812N do not evoke ECAPs
that are detectible by IMD 200. Although control pulses 812B emit
ECAPs 836B, which are detectible by IMD 200, it may be the case
that IMD 200 does not sense enough detectible ECAPs for therapy
determination in the example of FIG. 8. As such, IMD 200 may
determine one or more characteristics of stimulation signals 838 in
order to determine one or more parameters of upcoming stimulation
pulses following control pulses 812N.
[0146] FIG. 9 is a flow diagram illustrating an example operation
for controlling stimulation based on one or more sensed ECAPs, in
accordance with one or more techniques of this disclosure. For
convenience, FIG. 9 is described with respect to IMD 200 of FIG. 2.
However, the techniques of FIG. 9 may be performed by different
components of IMD 200 or by additional or alternative medical
devices.
[0147] Stimulation generation circuitry 202 of IMD 200 may deliver
electrical stimulation therapy to a patient (e.g., patient 105). In
order to control the electrical stimulation therapy, processing
circuitry 210 may direct the delivery of at least some stimulation
pulses according to therapy stimulation programs 214 of storage
device 212, where the electrical stimulation therapy may include a
plurality of control pulses and/or informed pulses. Informed pulses
may, in some cases, produce ECAPs detectable by IMD 200. However,
in other cases, an electrical polarization of an informed pulse may
interfere with sensing of an ECAP responsive to the informed pulse.
In some examples, to evoke ECAPs which are detectable by IMD 200,
stimulation generation circuitry 202 delivers a plurality of
control pulses, the plurality of control pulses being interleaved
with at least some informed pulses of the plurality of informed
pulses. Processing circuitry 210 may control the delivery of
control pulses according to ECAP test stimulation programs 216.
Since the control pulses may be interleaved with the informed
pulses, sensing circuitry 206 of IMD 200 may detect a plurality of
ECAPs, where sensing circuitry 206 is configured to detect each
ECAP of the plurality of ECAPs after a control pulse of the
plurality of control pulses and prior to a subsequent informed
pulse of the plurality of informed pulses. In this way, IMD 200 may
evoke the plurality of ECAPs in target tissue by delivering control
pulses without the informed pulses obstructing IMD 200 from sensing
the ECAPs.
[0148] As illustrated in FIG. 9, processing circuitry 210 directs
stimulation generation circuitry 202 to deliver a control pulse
(902). Stimulation generation circuitry 202 may deliver the control
pulse to target tissue of patient 105 via any combination of
electrodes 232, 234 of leads 230. In some examples, the control
pulse may include a balanced, bi-phasic square pulse that employs
an active recharge phase. However, in other examples, the control
pulse may include a monophasic pulse followed by a passive recharge
phase. In other examples, the control pulse may include an
imbalanced bi-phasic portion and a passive recharge portion.
Although not necessary, a bi-phasic control pulse may include an
interphase interval between the positive and negative phase to
promote propagation of the nerve impulse in response to the first
phase of the bi-phasic pulse. The control pulse may have a pulse
width of 300 .mu.s, such as a bi-phasic pulse with each phase
having a duration of approximately 100 .mu.s.
[0149] After delivering the control pulse, IMD 200 attempts to
detect an ECAP (904). For example, sensing circuitry 206 may
monitor signals from any combination of electrodes 232, 234 of
leads 230. In some examples, sensing circuitry 206 detects ECAPs
from a particular combination of electrodes 232, 234. In some
cases, the particular combination of electrodes for sensing ECAPs
includes different electrodes than a set of electrodes 232, 234
used to deliver stimulation pulses. Alternatively, in other cases,
the particular combination of electrodes used for sensing ECAPs
includes at least one of the same electrodes as a set of electrodes
used to deliver stimulation pulses to patient 105. In some
examples, the particular combination of electrodes used for sensing
ECAPs may be located on an opposite side of leads 230 from the
particular combination of electrodes used to deliver stimulation
pulses. IMD 200 may detect an ECAP responsive to the control pulse.
IMD 200 may measure one or more characteristics of the responsive
ECAP, such as ECAP amplitude, ECAP duration, peak-to-peak
durations, or any combination thereof. For example, to measure an
amplitude of the ECAP, IMD 200 may determine a voltage difference
between an N1 ECAP peak and a P2 ECAP peak.
[0150] At block 906, processing circuitry 210 determines if the
ECAP amplitude of the responsive ECAP is greater than an ECAP
amplitude threshold. If the ECAP amplitude is greater than the ECAP
amplitude threshold ("YES" branch of block 906), processing
circuitry 210 activates/continues a decrement mode (908) in IMD
200. For example, if the decrement mode is already "turned on" in
IMD 200 when processing circuitry determines that the ECAP
amplitude is greater than the ECAP amplitude threshold, then
processing circuitry 210 maintains IMD 200 in the decrement mode.
If the decrement mode is "turned off" in IMD 200 when processing
circuitry determines that the ECAP amplitude is greater than the
ECAP amplitude threshold, then processing circuitry 210 activates
the decrement mode. In some examples, the decrement mode may be
stored in storage device 212 as a part of control policy 213. The
decrement mode may be a set of instructions which causes IMD 200 to
decrease one or more parameter values of each consecutive informed
pulse from a respective predetermined value (e.g., a value
determined by a stimulation program) and decrease one or more
parameter values of each consecutive control pulse from a
respective predetermined value (e.g., a value determined by a
stimulation program). In other words, the parameter values may be
reduced from the values that IMD 200 would use to define respective
pulses in the absence of the ECAP amplitude exceeding the threshold
ECAP amplitude. For example, when the decrement mode is activated,
processing circuitry 210 may decrease an electric current amplitude
of each consecutive informed pulse delivered by IMD 200 and
decrease an electric current amplitude of each consecutive control
pulse delivered by IMD 200. After processing circuitry 210
activates/continues the decrement mode, the example operation may
return to block 902 and IMD 200 may deliver another control
pulse.
[0151] If the ECAP amplitude is not greater than the ECAP amplitude
threshold ("NO" branch of block 906), processing circuitry 210
determines whether the decrement mode is activated in IMD 200
(910). If the decrement mode is activated in IMD 200 ("YES" branch
of block 910), processing circuitry 210 deactivates the decrement
mode and activates an increment mode (912) in IMD 200. In some
examples, the increment mode may be stored in storage device 212 as
a part of control policy 213. The increment mode may be a set of
instructions which causes IMD 200 to increase one or more parameter
values of each consecutive informed pulse and increase one or more
parameter values of each consecutive control pulse. For example,
when the increment mode is activated, processing circuitry 210 may
increase an electric current amplitude of each consecutive informed
pulse delivered by IMD 200 and increase an electric current
amplitude of each consecutive control pulse delivered by IMD 200.
After processing circuitry 210 deactivates the decrement mode and
activates the increment mode, the example operation may return to
block 902 and IMD 200 may deliver another control pulse.
[0152] When the example operation of FIG. 9 arrives at block 910
and the decrement mode is not activated in IMD 200 ("NO" branch of
block 910), processing circuitry 210 determines whether the
increment mode is activated (914) in IMD 200. If the increment mode
is activated in IMD 200 ("YES" branch of block 914), processing
circuitry 210 may complete the increment mode (916) in IMD 200. In
some examples, to complete the increment mode, processing circuitry
210 may increase the electric current amplitude of each consecutive
informed pulse delivered by IMD 200 and increase the electric
current amplitude of each consecutive control pulse delivered by
IMD 200 until the pulse amplitude of the stimulation pulses reach
an electric current amplitude (e.g., a predetermined value that may
be set by the stimulation program selected for therapy) of the
stimulation pulses delivered by IMD 200 prior to the activation of
the decrement mode. In this manner, the process may not be referred
to as a fully closed-loop system. Put another way, IMD 200 may
monitor the high end (ECAP amplitude threshold) for adjusting
stimulation pulses instead of monitoring any low end of the sensed
ECAP amplitude. For example, IMD 200 may continue to increase the
current amplitude of consecutive informed pulses without any
feedback from the sensed ECAP, unless the sensed ECAP value again
exceeds the ECAP amplitude threshold. After processing circuitry
210 completes the increment mode, the example operation may return
to block 902 and IMD 200 may deliver another control pulse. When
the example operation of FIG. 9 arrives at block 914 and the
increment mode is not activated in IMD 200 ("NO" branch of block
914), processing circuitry 210 maintains stimulation (918) in IMD
200. Although FIG. 9 describes adjusting both informed pulses and
control pulses, the technique of FIG. 9 may also apply when IMD 200
is delivering only control pulses (e.g., without informed pulses)
to the patient for therapy.
[0153] FIG. 10 illustrates a voltage/current/time graph 1000 which
plots control pulse current amplitude 1002, informed pulse current
amplitude 1004, ECAP voltage amplitude 1008, and second ECAP
voltage amplitude 1010 as a function of time, in accordance with
one or more techniques of this disclosure. Additionally, FIG. 10
illustrates a threshold ECAP amplitude 1006. For convenience, FIG.
10 is described with respect to IMD 200 of FIG. 2. However, the
techniques of FIG. 10 may be performed by different components of
IMD 200 or by additional or alternative medical devices.
[0154] Voltage/current/time graph 1000 illustrates a relationship
between sensed ECAP voltage amplitude and stimulation current
amplitude. For example, control pulse current amplitude 1002 and
informed pulse current amplitude 1004 are plotted alongside ECAP
voltage amplitude 1008 as a function of time, thus showing how
stimulation current amplitude changes relative to ECAP voltage
amplitude. In some examples, IMD 200 delivers a plurality of
control pulses and a plurality of informed pulses at control pulse
current amplitude 1002 and informed pulse current amplitude 1004,
respectively. Initially, IMD 200 may deliver a first set of control
pulses, where IMD 200 delivers the first set of control pulses at
current amplitude I2. Additionally, IMD 200 may deliver a first set
of informed pulses, where IMD 200 delivers the first set of control
pulses at current amplitude I1. I1 and I2 may be referred to as a
predetermined value for the amplitude of respective control and
informed pulses. This predetermined value may be a programmed value
or otherwise selected value that a stimulation program has selected
to at least partially define stimulation pulses to the patient in
the absence of transient conditions (e.g., when the ECAP amplitude
is below a threshold ECAP value). The first set of control pulses
and the first set of informed pulses may be delivered prior to time
T1. In some examples, I1 is 4 milliamps (mA) and I2 is 8 mA.
Although control pulse current amplitude 1002 is shown as greater
than informed pulse current amplitude 1004, control pulse current
amplitude 1002 may be less than or the same as informed pulse
current amplitude 1004 in other examples.
[0155] While delivering the first set of control pulses and the
first set of informed pulses, IMD 200 may record ECAP voltage
amplitude 1008. During dynamic and transient conditions which occur
in patient 105 such as coughing, sneezing, laughing, Valsalva
maneuvers, leg lifting, cervical motions, or deep breathing, ECAP
voltage amplitude 1008 may increase if control pulse current
amplitude 1002 and informed pulse current amplitude 1004 are held
constant. This increase in ECAP voltage amplitude 1008 may be
caused by a reduction in the distance between the electrodes and
nerves. For example, as illustrated in FIG. 10, ECAP voltage
amplitude 1008 may increase prior to time T1 while stimulation
current amplitude is held constant. An increasing ECAP voltage
amplitude 1008 may indicate that patient 105 is at risk of
experiencing transient overstimulation due to the control pulses
and the informed pulses delivered by IMD 200. To prevent patient
105 from experiencing transient overstimulation, IMD 200 may
decrease control pulse current amplitude 1002 and informed pulse
current amplitude 1004 in response to ECAP voltage amplitude 1008
exceeding the threshold ECAP amplitude 1006. For example, if IMD
200 senses an ECAP having an ECAP voltage amplitude 1008 meeting or
exceeding threshold ECAP amplitude 1006, as illustrated in FIG. 10
at time T1, IMD 200 may enter a decrement mode where control pulse
current amplitude 1002 and informed pulse current amplitude 1004
are decreased. In some examples, the threshold ECAP amplitude 1006
is selected from a range of approximately 5 microvolts (.mu.V) to
approximately 30 .mu.V, or from a range of approximately 10
microvolts (.mu.V) to approximately 20 .mu.V. For example, the
threshold ECAP amplitude 1006 is 15 .mu.V. In other examples, the
threshold ECAP amplitude 1006 is less than or equal to 5 .mu.V or
greater than or equal to 30 .mu.V.
[0156] IMD 200 may respond relatively quickly to the ECAP voltage
amplitude 1008 exceeding the threshold ECAP amplitude 1006. For
example, IMD may be configured to detect threshold exceeding ECAP
amplitudes within 20 milliseconds (ms). If IMD 200 delivers control
pulses at a frequency of 50 Hz, the period of time for a single
sample that includes delivering the control pulse and detecting the
resulting ECAP signal may be 20 ms or less. However, since an ECAP
signal may occur within one or two ms of delivery of the control
pulse, IMD 200 may be configured to detect an ECAP signal exceeding
the threshold ECAP amplitude in less than 10 ms. For transient
conditions, such as a patient coughing or sneezing, these sampling
periods would be sufficient to identify ECAP amplitudes exceeding
the threshold and a responsive reduction in subsequent pulse
amplitudes before the ECAP amplitude would have reached higher
levels that may have been uncomfortable for the patient.
[0157] The decrement mode may, in some cases, be stored in storage
device 212 of IMD 200 as a part of control policy 213. In the
example illustrated in FIG. 10, the decrement mode is executed by
IMD 200 over a second set of control pulses and a second set of
informed pulses which occur between time T1 and time T2. In some
examples, to execute the decrement mode, IMD 200 decreases the
control pulse current amplitude 1002 of each control pulse of the
second set of control pulses according to a first function with
respect to time. In other words, IMD 200 decreases each consecutive
control pulse of the second set of control pulses proportionally to
an amount of time elapsed since a previous control pulse.
Additionally, during the decrement mode, IMD 200 may decrease the
informed pulse current amplitude 1004 of each informed pulse of the
second set of informed pulses according to a second function with
respect to time. Although linear first and second functions are
shown, the first and/or second function may be non-linear, such as
logarithmic (e.g., the rate of change decreases over time),
exponential (e.g., the rate of change increases over time),
parabolic, step-wise, multiple different functions, etc., in other
examples. During a period of time in which IMD 200 is operating in
the decrement mode (e.g., time interval T2-T1), ECAP voltage
amplitude 1008 of ECAPs sensed by IMD 200 may be greater than or
equal to threshold ECAP amplitude 1006.
[0158] In the example illustrated in FIG. 2, IMD 200 may sense an
ECAP at time T2, where the ECAP has an ECAP voltage amplitude 1008
that is less than threshold ECAP amplitude 1006. The ECAP sensed at
time T2 may, in some cases, be the first ECAP sensed by IMD 200
with a below-threshold amplitude since IMD 200 began the decrement
mode at time T1. Based on sensing the ECAP at time T2, IMD 200 may
deactivate the decrement mode and activate an increment mode. The
increment mode may, in some cases, be stored in storage device 212
of IMD 200 as a part of control policy 213. IMD 200 may execute the
increment mode over a third set of control pulses and a third set
of informed pulses which occur between time T2 and time T3. In some
examples, to execute the increment mode, IMD 200 increases the
control pulse current amplitude 1002 of each control pulse of the
third set of control pulses according to a third function with
respect to time. In other words, IMD 200 increases each consecutive
control pulse of the third set of control pulses proportionally to
an amount of time elapsed since a previous control pulse.
Additionally, during the increment mode, IMD 200 may increase the
informed pulse current amplitude 1004 of each informed pulse of the
third set of informed pulses according to a fourth function with
respect to time.
[0159] As shown in FIG. 10, IMD 200 is configured to decrease
amplitude at a faster rate than increasing amplitude after ECAP
voltage amplitude 1008 falls below threshold ECAP amplitude 1006.
In other examples, the rate of change during the decrement mode and
increment mode may be similar. In other examples, IMD 200 may be
configured to increase amplitude of informed and control pulses at
a faster rate than when decreasing amplitude. The rate of change in
amplitude of the pulses may be relatively instantaneously (e.g., a
very fast rate) in other examples. For example, in response to ECAP
voltage amplitude 1008 exceeding threshold ECAP amplitude 1006, IMD
200 may immediately drop the amplitude of one or both of control
pulse current amplitude 1002 or informed pulse current amplitude
1004 to a predetermined or calculated value. Then, in response to
ECAP voltage amplitude 1008 dropping back below threshold ECAP
amplitude 1006, IMD 200 may enter increment mode as described
above.
[0160] When control pulse current amplitude 1002 and informed pulse
current amplitude 1004 return to current amplitude I2 and current
amplitude I1, respectively, IMD 200 may deactivate the increment
mode and deliver stimulation pulses at constant current amplitudes.
By decreasing stimulation in response to ECAP amplitudes exceeding
a threshold and subsequently increasing stimulation in response to
ECAP amplitudes falling below the threshold, IMD 200 may prevent
patient 105 from experiencing transient overstimulation or decrease
a severity of transient overstimulation experienced by patient 105,
whether the decrease is in terms of the length of the experience,
the relative intensity, or both.
[0161] FIG. 10 is described in the situation in which IMD 200
delivers both control pulse and informed pulses. However, IMD 200
may apply the technique of FIG. 10 to the situation in which only
control pulses are delivered to provide therapy to the patient. In
this manner, IMD 200 would similarly enter a decrement mode or
increment mode for control pulse current amplitude 1002 based on
the detected ECAP voltage amplitude 1008 without adjusting the
amplitude or other parameter of any other type of stimulation
pulse.
[0162] FIG. 11 is a flow diagram illustrating an example operation
for controlling stimulation based on one or more sensed ECAPs, in
accordance with one or more techniques of this disclosure. FIG. 11
is similar to FIG. 9 above, except that FIG. 11 employs a buffer
defined by an upper threshold and a lower threshold that define
when amplitude values are increased or decreased. For convenience,
FIG. 11 is described with respect to IMD 200 of FIG. 2. However,
the techniques of FIG. 11 may be performed by different components
of IMD 200 or by additional or alternative medical devices.
[0163] Stimulation generation circuitry 202 of IMD 200 may deliver
electrical stimulation therapy to a patient (e.g., patient 105). In
order to control the electrical stimulation therapy, processing
circuitry 210 may direct the delivery of at least some stimulation
pulses according to therapy stimulation programs 214 of storage
device 212, where the electrical stimulation therapy may include a
plurality of control pulses and/or informed pulses. Informed pulses
may, in some cases, produce ECAPs detectable by IMD 200. However,
in other cases, an electrical polarization of an informed pulse may
interfere with sensing of an ECAP responsive to the informed pulse.
In some examples, to evoke ECAPs which are detectable by IMD 200,
stimulation generation circuitry 202 delivers a plurality of
control pulses, the plurality of control pulses being interleaved
with at least some informed pulses of the plurality of informed
pulses. Processing circuitry 210 may control the delivery of
control pulses according to ECAP test stimulation programs 216.
Since the control pulses may be interleaved with the informed
pulses, sensing circuitry 206 of IMD 200 may detect a plurality of
ECAPs, where sensing circuitry 206 is configured to detect each
ECAP of the plurality of ECAPs after a control pulse of the
plurality of control pulses and prior to a subsequent informed
pulse of the plurality of informed pulses. In this way, IMD 200 may
evoke the plurality of ECAPs in target tissue by delivering control
pulses without the informed pulses obstructing IMD 200 from sensing
the ECAPs.
[0164] As illustrated in FIG. 11, processing circuitry 210 directs
stimulation generation circuitry 202 to deliver a control pulse
(1102). Stimulation generation circuitry 202 may deliver the
control pulse to target tissue of patient 105 via any combination
of electrodes 232, 234 of leads 230. In some examples, the control
pulse may include a balanced, bi-phasic square pulse that employs
an active recharge phase. However, in other examples, the control
pulse may include a monophasic pulse followed by a passive recharge
phase. In other examples, the control pulse may include an
imbalanced bi-phasic portion and a passive recharge portion.
Although not necessary, a bi-phasic control pulse may include an
interphase interval between the positive and negative phase to
promote propagation of the nerve impulse in response to the first
phase of the bi-phasic pulse. The control pulse may have a pulse
width of approximately 300 .mu.s, such as a bi-phasic pulse with
each phase having a duration of approximately 100 .mu.s.
[0165] After delivering the control pulse, IMD 200 attempts to
detect an ECAP (1104). For example, sensing circuitry 206 may
monitor signals from any combination of electrodes 232, 234 of
leads 230. In some examples, sensing circuitry 206 detects ECAPs
from a particular combination of electrodes 232, 234. In some
cases, the particular combination of electrodes for sensing ECAPs
includes different electrodes than a set of electrodes 232, 234
used to deliver stimulation pulses. Alternatively, in other cases,
the particular combination of electrodes used for sensing ECAPs
includes at least one of the same electrodes as a set of electrodes
used to deliver stimulation pulses to patient 105. In some
examples, the particular combination of electrodes used for sensing
ECAPs may be located on an opposite side of leads 230 from the
particular combination of electrodes used to deliver stimulation
pulses. IMD 200 may detect an ECAP responsive to the control pulse.
IMD 200 may measure one or more characteristics of the responsive
ECAP, such as ECAP amplitude, ECAP duration, peak-to-peak
durations, or any combination thereof. For example, to measure an
amplitude of the ECAP, IMD 200 may determine a voltage difference
between an N1 ECAP peak and a P2 ECAP peak.
[0166] At block 1106, processing circuitry 210 determines if the
ECAP amplitude of the responsive ECAP is greater than an upper ECAP
amplitude threshold. If the ECAP amplitude is greater than the
upper ECAP amplitude threshold ("YES" branch of block 1106),
processing circuitry 210 activates/continues a decrement mode
(1108) in IMD 200. For example, if the decrement mode is already
"turned on" in IMD 200 when processing circuitry determines that
the ECAP amplitude is greater than the upper ECAP amplitude
threshold, then processing circuitry 210 maintains IMD 200 in the
decrement mode. If the decrement mode is "turned off" in IMD 200
when processing circuitry determines that the ECAP amplitude is
greater than the upper ECAP amplitude threshold, then processing
circuitry 210 activates the decrement mode to reduce the pulse
amplitude from a predetermined value programmed for stimulation. In
some examples, the decrement mode may be stored in storage device
212 as a part of control policy 213. The decrement mode may be a
set of instructions which causes IMD 200 to decrease one or more
parameter values of each consecutive informed pulse and decrease
one or more parameter values of each consecutive control pulse. For
example, when the decrement mode is activated, processing circuitry
210 may decrease an electric current amplitude of each consecutive
informed pulse delivered by IMD 200 and decrease an electric
current amplitude of each consecutive control pulse delivered by
IMD 200. After processing circuitry 210 activates/continues the
decrement mode, the example operation may return to block 1102 and
IMD 200 may deliver another control pulse.
[0167] If the ECAP amplitude is not greater than the ECAP amplitude
threshold ("NO" branch of block 1106), processing circuitry 210
determines whether the ECAP amplitude is less than a lower ECAP
amplitude threshold in block 1110. If the ECAP amplitude is less
than the lower ECAP amplitude threshold ("YES" branch of block
1110), processing circuitry 210 activates an increment mode (1112)
in IMD 200. In some examples, the increment mode may be stored in
storage device 212 as a part of control policy 213. The increment
mode may be a set of instructions which causes IMD 200 to increase
one or more parameter values of each consecutive informed pulse and
increase one or more parameter values of each consecutive control
pulse. For example, when the increment mode is activated,
processing circuitry 210 may increase an electric current amplitude
of each consecutive informed pulse delivered by IMD 200 and
increase an electric current amplitude of each consecutive control
pulse delivered by IMD 200. After processing circuitry 210
activates the increment mode, the example operation may return to
block 1102 and IMD 200 may deliver another control pulse.
Processing circuitry 210 may continue to increment the pulse
amplitude until the pulse amplitude returns to the predetermined
value of the amplitude programmed for delivery prior to the ECAP
amplitude exceeding the upper ECAP amplitude threshold.
[0168] If the ECAP amplitude is not less than the lower ECAP
amplitude threshold ("NO" branch of block 1110), processing
circuitry 1114 maintains the pulse amplitude currently used to at
least partially define parameter values. In this manner, when the
ECAP amplitude is between the upper ECAP amplitude threshold and
the lower ECAP amplitude threshold, processing circuitry 210 does
not increase the amplitude value back to the predetermined value or
decreased the amplitude. This "buffer" zone may reduce oscillating
amplitude values when the ECAP amplitudes are similar to the ECAP
amplitude threshold. These oscillating amplitude values may be
perceived as uncomfortable or unwanted by the patient. However,
once the ECAP amplitude drops below the lower ECAP amplitude
threshold, processing circuitry 210 can return the amplitude value
back to the predetermined amplitude value intended for therapy.
[0169] In some examples, the upper ECAP amplitude threshold and the
lower ECAP amplitude threshold are defined. In other examples,
processing circuitry 210 may define the upper ECAP amplitude
threshold and/or the lower ECAP amplitude threshold as a buffer or
deviation from a single defined ECAP threshold value. For example,
processing circuitry 210 may define the lower ECAP amplitude
threshold based on an upper ECAP amplitude threshold defined by a
user or calculated from initial patient perception thresholds
and/or discomfort thresholds. Although FIG. 11 describes adjusting
amplitudes for both informed pulses and control pulses, the
technique of FIG. 11 may also apply when IMD 200 is delivering only
control pulses (e.g., without informed pulses) to the patient for
therapy.
[0170] FIG. 12 illustrates a voltage/current/time graph 1200 which
plots control pulse current amplitude 1202, informed pulse current
amplitude 1204, and ECAP voltage amplitude 1210 as a function of
time, in accordance with one or more techniques of this disclosure.
Additionally, FIG. 12 illustrates upper threshold ECAP amplitude
1206 and lower threshold ECAP amplitude 1208. FIG. 12 may be
similar to FIG. 10, but FIG. 12 illustrates a technique in which
two thresholds for ECAP voltage amplitude 1210 are employed to
provide a buffer that may reduce possible oscillations in pulse
amplitude if the ECAP amplitude oscillates near a single ECAP
amplitude threshold. For convenience, FIG. 10 is described with
respect to IMD 200 of FIG. 2. However, the techniques of FIG. 12
may be performed by different components of IMD 200 or by
additional or alternative medical devices.
[0171] Voltage/current/time graph 1200 illustrates a relationship
between sensed ECAP voltage amplitude and stimulation current
amplitude. For example, control pulse current amplitude 1202 and
informed pulse current amplitude 1204 are plotted alongside ECAP
voltage amplitude 1210 as a function of time, thus showing how IMD
200 is configured to change stimulation current amplitude relative
to detected ECAP voltage amplitude (or some other ECAP
characteristic value). In some examples, IMD 200 delivers a
plurality of control pulses and a plurality of informed pulses at
control pulse current amplitude 1202 and informed pulse current
amplitude 1204, respectively. Initially, IMD 200 may deliver a
first set of control pulses, where IMD 200 delivers the first set
of control pulses at current amplitude I2. Additionally, IMD 200
may deliver a first set of informed pulses, where IMD 200 delivers
the first set of informed pulses at current amplitude I1. I1 and I2
may be referred to as a predetermined value for the amplitude of
respective control and informed pulses. This predetermined value
may be a programmed value or otherwise selected value that a
stimulation program has selected to at least partially define
stimulation pulses to the patient in the absence of transient
conditions (e.g., when the ECAP amplitude is below a threshold ECAP
value). The first set of control pulses and the first set of
informed pulses may be delivered prior to time T1. In some
examples, I1 is 4 milliamps (mA) and I2 is 8 mA. Although informed
pulse current amplitude 1202 is shown as greater than control pulse
current amplitude 1204, informed pulse current amplitude 1202 may
be less than or the same as control pulse current amplitude 1204 in
other examples.
[0172] While delivering the first set of control pulses and the
first set of informed pulses, IMD 200 may determine ECAP voltage
amplitude 1210 from respective ECAP signals. During dynamic and
transient conditions which occur in patient 105 such as coughing,
sneezing, laughing, Valsalva maneuvers, leg lifting, cervical
motions, or deep breathing, ECAP voltage amplitude 1210 may
increase if control pulse current amplitude 1202 and informed pulse
current amplitude 1204 are held constant. This increase in ECAP
voltage amplitude 1210 may be caused by a reduction in the distance
between the electrodes and nerves. For example, as illustrated in
FIG. 12, ECAP voltage amplitude 1208 may increase prior to time T1
while stimulation current amplitude is held constant. An increasing
ECAP voltage amplitude 1208 may indicate that patient 105 is at
risk of experiencing transient overstimulation due to the control
pulses and the informed pulses delivered by IMD 200. However, IMD
200 may not take any action until ECAP voltage amplitude 1210
exceeds, or is greater than, upper threshold ECAP amplitude 1206.
To prevent patient 105 from experiencing transient overstimulation,
IMD 200 may decrease control pulse current amplitude 1202 and
informed pulse current amplitude 1204 in response to ECAP voltage
amplitude 12010 exceeding the upper threshold ECAP amplitude 1206.
For example, if IMD 200 senses an ECAP having an ECAP voltage
amplitude 1210 meeting or exceeding upper threshold ECAP amplitude
1206, as illustrated in FIG. 12 at time T1, IMD 200 may enter a
decrement mode where IMD 200 decreases control pulse current
amplitude 1202 and informed pulse current amplitude 1204. In some
examples, the upper threshold ECAP amplitude 1206 is selected from
a range of approximately 5 microvolts (Or) to approximately 30
.mu.V, or from a range of approximately 10 microvolts (Or) to
approximately 20 .mu.V. For example, the upper threshold ECAP
amplitude 1206 is 15 .mu.N. In other examples, the upper threshold
ECAP amplitude 1206 is less than or equal to 5 .mu.V or greater
than or equal to 30 .mu.V. In some examples, IMD 200 may determine
upper threshold ECAP amplitude 1206 from a target threshold, such
that upper threshold ECAP amplitude 1206 is above the target
threshold and lower threshold ECAP amplitude 1208 is below the
target threshold.
[0173] IMD 200 may respond relatively quickly to the ECAP amplitude
1210 exceeding the upper threshold ECAP amplitude 1206. For
example, IMD may be configured to detect threshold exceeding ECAP
amplitudes within 20 milliseconds (ms). If IMD 200 delivers control
pulses at a frequency of 50 Hz, the period of time for a single
sample that includes delivering the control pulse and detecting the
resulting ECAP signal may be 20 ms or less. However, since an ECAP
signal may occur within one or two ms of delivery of the control
pulse, IMD 200 may be configured to detect an ECAP signal exceeding
the threshold ECAP amplitude in less than 10 ms. For transient
conditions, such as a patient coughing or sneezing, these sampling
periods would be sufficient to identify ECAP amplitudes exceeding
the threshold and a responsive reduction in subsequent pulse
amplitudes before the ECAP amplitude would have reached higher
levels that may have been uncomfortable for the patient.
[0174] The decrement mode may, in some cases, be stored in storage
device 212 of IMD 200 as a part of control policy 213. In the
example illustrated in FIG. 10, the decrement mode is executed by
IMD 200 over a second set of control pulses and a second set of
informed pulses which occur between time T1 and time T2. In some
examples, to execute the decrement mode, IMD 200 decreases the
control pulse current amplitude 1202 of each control pulse of the
second set of control pulses according to a first function with
respect to time. In other words, IMD 200 decreases each consecutive
control pulse of the second set of control pulses proportionally to
an amount of time elapsed since a previous control pulse.
Additionally, during the decrement mode, IMD 200 may decrease the
informed pulse current amplitude 1204 of each informed pulse of the
second set of informed pulses according to a second function with
respect to time. Although linear first and second functions are
shown, the first and/or second function may be non-linear, such as
logarithmic (e.g., the rate of change decreases over time),
exponential (e.g., the rate of change increases over time),
parabolic, step-wise, multiple different functions, etc., in other
examples. During a period of time in which IMD 200 is operating in
the decrement mode (e.g., time interval T2-T1), ECAP voltage
amplitude 1210 of ECAPs sensed by IMD 200 may be greater than or
equal to upper threshold ECAP amplitude 1206.
[0175] In the example illustrated in FIG. 12, IMD 200 may sense an
ECAP at time T2, where the ECAP has an ECAP voltage amplitude 1210
that is less than upper threshold ECAP amplitude 1206. However,
ECAP voltage amplitude 1210 may still be greater than lower
threshold ECAP amplitude 1208. Within this zone between upper
threshold ECAP amplitude 1206 and lower threshold ECAP amplitude
1208, IMD 200 may maintain control pulse current amplitude 1202 and
informed pulse current amplitude 1204 (e.g., between T2 and T3). By
not immediately increasing the amplitudes for both control pulse
current amplitude 1202 and informed pulse current amplitude 1204 in
response to ECAP voltage amplitude 1210 dropping below upper
threshold ECAP amplitude 1206, IMD 200 may prevent these pulse
amplitudes from increasing again only to be subjected to another
spike in ECAP voltage amplitude 1210. These subsequent spikes could
be perceived by the patient has undesirable waves or oscillations
in therapy intensity. Lower threshold ECAP amplitude 1208 may be
set as a percentage of, or absolute value below, upper threshold
ECAP amplitude 1206 or a target threshold. In some examples, the
zone between upper threshold ECAP amplitude 1206 and lower
threshold ECAP amplitude 1208 may have a predetermined magnitude
and/or be adjustable by a patient or physician. For example, upper
threshold ECAP amplitude 1206 and/or lower threshold ECAP amplitude
1208 may be adjusted to increase the zone if the patient still
experiences oscillations in therapy intensity.
[0176] At T3, IMD 200 may again detect that ECAP voltage amplitude
1210 exceeds upper threshold ECAP amplitude 1206 and responsively
decrease control pulse current amplitude 1202 and informed pulse
current amplitude 1204 even further. At time T4, ECAP voltage
amplitude 1210 drops below upper threshold ECAP amplitude 1206 but
is still greater than lower threshold ECAP amplitude 1208.
Therefore, between times T4 and T5, IMD 200 may maintain control
pulse current amplitude 1202 and informed pulse current amplitude
1204. At time T5, IMD 200 determines that ECAP voltage amplitude
1210 drops below and is less than lower threshold ECAP amplitude
1208. In response to ECAP voltage amplitude 1210 dropping below
lower threshold ECAP amplitude 1208, IMD 200 may begin to increase
control pulse current amplitude 1202 and informed pulse current
amplitude 1204 back up to the respective predetermined values I1
and I2 at time T6. If ECAP voltage amplitude 1210 would have again
exceeded upper threshold ECAP amplitude 1206 before time T6, IMD
200 would have reduced control pulse current amplitude 1202 and
informed pulse current amplitude 1204 as discussed above with
respect to the time period between T1 and T2.
[0177] The rate of change in amplitude of the pulses may be
relatively instantaneously (e.g., a very fast rate) in other
examples. For example, in response to ECAP voltage amplitude 1210
exceeding upper threshold ECAP amplitude 1206, IMD 200 may
immediately drop the amplitude of one or both of control pulse
current amplitude 1202 or informed pulse current amplitude 1204 to
a predetermined or calculated value. Then, in response to ECAP
voltage amplitude 1210 dropping back below lower threshold ECAP
amplitude 1208, IMD 200 may enter increment mode as described
above.
[0178] When control pulse current amplitude 1002 and informed pulse
current amplitude 1004 return to current amplitude I2 and current
amplitude I1 (e.g., the predetermined value or programmed value for
each type pulse), respectively, IMD 200 may deactivate the
increment mode and deliver stimulation pulses at constant current
amplitudes once again. By decreasing stimulation in response to
ECAP amplitudes exceeding the upper threshold and subsequently
increasing stimulation in response to ECAP amplitudes falling below
the lower threshold, IMD 200 may prevent patient 105 from
experiencing transient overstimulation or decrease a severity of
transient overstimulation experienced by patient 105, while also
reducing potential oscillations that could occur with a single
threshold, whether the decrease is in terms of the length of the
experience, the relative intensity, or both.
[0179] FIG. 12 is described in the situation in which IMD 200
delivers both control pulse and informed pulses. However, IMD 200
may apply the technique of FIG. 10 to the situation in which only
control pulses are delivered to provide therapy to the patient and
elicit detectable ECAP signals. In this manner, IMD 200 would
similarly enter a decrement mode or increment mode for control
pulse current amplitude 1202 based on the detected ECAP voltage
amplitude 1210 without adjusting the amplitude or other parameter
of any other type of stimulation pulse.
[0180] FIG. 13 is a block diagram illustrating a system 1300 for
determining a control policy 1300 of an IMD, in accordance with one
or more techniques of this disclosure. As seen in FIG. 13, system
1300 includes user interface 1302, control policy monitor unit
1310, diagnostics/debug unit 1320, state classification unit 1330,
control policy unit 1340, and stimulation configuration unit
1350.
[0181] In some examples, state classification unit 1330 may
estimate the state of a monitored system based on input data. For
example, ECAPs may represent inputs to state classification unit
1330 to estimate tissue activation (e.g., ECAP characteristic
values) during the delivery of one or more stimulation pulses to
target tissue of a patient (e.g., spinal cord 120 of patient 105).
State classification unit 1330 may generate one or more outputs for
sending to control policy unit 1340. In turn, control policy unit
1340 may receive the one or more outputs from state classification
unit 1330 and receive one or more additional inputs from other
parts of the system or external sources (e.g., conditioned signals,
patient input, control policy monitor unit 1310). Control policy
unit 1340 may determine a control policy based on the received
inputs, where the control policy drives one or more therapy
configuration updates at stimulation configuration unit 1350. It
may be beneficial to make adjustments to state classification unit
1330 and control policy unit 1340 as patient symptoms and other
factors change (e.g., lead migration).
[0182] System 1300 may monitor attributes of input data (e.g.,
outputs of state classification unit 1330 and outputs of control
policy monitor unit 1310) and generate a control policy in order to
improve a performance of IMD 110 as compared with systems that do
not use input data to determine a control policy. For example,
system 1300 may decrease a number of patient interactions required
to update a system configuration and decrease a number of sudden
unwanted changes in a perceived level of paresthesia delivered by
IMD 110 (e.g., transient overstimulation events) as compared with
systems that do not determine control policy based on measured
signals. Additionally, control policy unit 1340 may adjust
stimulation delivered by IMD 110 based on a time of day.
[0183] As seen in FIG. 13, input signals, e.g., physiological
signals 1332 and inertial signals 1336, may be conditioned by
signal conditioning unit 1334 and signal conditioning unit 1338,
respectively. In some examples, physiological signals 1332 may
include cardiac signals (e.g., heart rate, heart rate variability,
blood pressure, and blood pressure variability), respiratory
signals (e.g., respiratory rate and respiratory rate variability),
and ECAPs. In some examples, inertial signals 1336 may include
accelerometer data and/or gyroscope data which indicate patient
motion and patient posture. During conditioning, one or more
features may be calculated to identify one or more attributes of
the input signals. State classification unit 1330 may use these
attributes to categorize a state of stimulation delivered by IMD
110 (e.g., too much tissue or too little tissue activated). The
determined state may be leveraged as an input to the control policy
determined by control policy unit 1340. Other inputs to the control
policy unit 1340 may include one or more user inputs from user
interface 1302 and one or more inputs from control policy monitor
unit 1310. After control policy unit 1340 determines a control
policy based on the inputs, control policy unit 1340 may output an
instruction to set one or more stimulation parameters using
stimulation configuration unit 1350.
[0184] In some examples, one or more configurable parameters that
define the control policy can be determined by control policy unit
1340. The one or more parameters may include, for example, an upper
bound and a lower bound of a buffer zone, an overstimulation
threshold, a maximum stimulation amplitude, a minimum stimulation
amplitude, a stimulation increment step size, a stimulation
increment step duration, a stimulation decrement step size, a
stimulation decrement step duration, and a scaling factor between
control pulse amplitude and informed pulse amplitude. The
attributes monitored by control policy monitor unit 1310 may
include, for example, any one or combination of a number of state
changes within a period of time, a number, frequency, or time of
day of patient adjustments, a lack of control policy state changes,
reported undesirable stimulation events, and changes in stimulation
amplitude.
[0185] In some examples, processing circuitry (e.g., processing
circuitry of IMD 110 and/or processing circuitry of external
programmer 150) may execute any one or combination of control
policy monitor unit 1310, diagnostics/debug unit 1320, state
classification unit 1330, control policy unit 1340, and stimulation
configuration unit 1350.
[0186] FIG. 14 is a flow diagram illustrating an example operation
for adjusting the control policy for IMD 110, in accordance with
one or more techniques of this disclosure. FIG. 14 is described
with respect to IMD 110, and external programmer 150 of FIG. 1, IMD
200 of FIG. 2, and external programmer 300 of FIG. 3. However, the
techniques of FIG. 14 may be performed by different components of
IMD 110, external programmer 150, IMD 200, and external programmer
300, or by additional or alternative medical devices.
[0187] Processing circuitry may record an occurrence of a
self-monitoring event and record one or more update settings (1402)
associated with the self-monitoring event. Processing circuitry may
determine whether a number of control policy state changes within a
first duration is greater than a threshold number of control policy
state changes (1404). When the number of control policy state
changes is greater than the threshold number of control policy
state changes ("YES" branch of block 1404), processing circuitry
may determine whether a patient indication of an undesired
paresthesia (1406) is received. When a patient indication of an
undesired paresthesia is not received ("NO" branch of block 1406),
processing circuitry may determine whether a patient indication of
a reduced therapeutic benefit is received (1408). When a patient
indication of a reduced therapeutic benefit is not received ("NO"
branch of block 1408), processing circuitry may determine that no
control policy changes are required.
[0188] When a patient indication of an undesired paresthesia is
received ("YES" branch of block 1406) or when a patient indication
of a reduced therapeutic benefit is received ("YES" branch of block
1408), processing circuitry may perform a lead integrity test of
one or more of leads 130 (1410). Subsequently, processing circuitry
\ may execute a "patient guidance wizard" algorithm (1412). After
executing the patient guidance wizard algorithm, processing
circuitry may recommend one or more control policy changes for
implementation by IMD 110.
[0189] When the number of control policy state changes is not
greater than the threshold number of control policy state changes
("NO" branch of block 1404), processing circuitry may determine
whether zero state changes occur during a second duration (1414).
If zero state changes occur during the second duration ("YES"
branch of block 1414), processing circuitry may perform the lead
integrity test (1410) on one or more of leads 130. If more than
zero state changes occur during the second duration ("NO" branch of
block 1414), processing circuitry determines whether a number of
patient parameter adjustments is greater than a threshold number of
patient parameter adjustments during a third duration (1416). If
the number of patient parameter adjustments is greater than the
threshold number of patient parameter adjustments during the third
duration ("YES" branch of block 1416), processing circuitry may
perform the lead integrity test (1410) on one or more of leads 130.
If the number of patient parameter adjustments is not greater than
the threshold number of patient parameter adjustments during the
third duration ("NO" branch of block 1416), external programmer 150
may determine whether an indication of an uncomfortable sensation
is received (1418). An uncomfortable sensation may be referred to
herein as a "zinger." Processing circuitry may be configured to
communicate with an external programmer, such as external
programmer 300 of FIG. 3. User interface 356 may receive a user
input indicating an undesirable attribute of a sensation and direct
the user input to processing circuitry.
[0190] When processing circuitry determines that indication of an
uncomfortable sensation is received ("YES" branch of block 1418),
processing circuitry outputs a request to record histogram data
stored by a rolling buffer (1420) of IMD 110. In some examples,
processing circuitry may receive the histogram data and analyze the
histogram data, which represents histogram data of a set of ECAPs
which are sensed by IMD 110 responsive to stimulation pulses
delivered by IMD 110. In order to analyze the histogram data,
processing circuitry may determine whether one or more ECAP
features exceed an ECAP feature threshold (1422). For example, if
the histogram data indicates that one or more ECAP features do not
exceed an ECAP feature threshold ("NO" branch of block 1422),
processing circuitry may initiate the patient guidance wizard
(1412) in order to obtain information relating to the uncomfortable
sensation indicated by the patient. When the histogram data
indicates that one or more ECAP features does exceed an ECAP
feature threshold ("YES" branch of block 1422), processing
circuitry may output a recommendation to change a control policy of
IMD 110 by increasing a decrement step size (1424) of one or more
stimulation pulses delivered by IMD 110. For example, IMD 110 may
be programmed to decrement stimulation pulses in response to
detecting an increase in ECAP amplitudes. By increasing the
decrement step size, processing circuitry may decrease a likelihood
that patient 105 experiences a transient overstimulation event in
the future.
[0191] When processing circuitry determines that indication of an
uncomfortable sensation is not received ("NO" branch of block
1418), processing circuitry may determine whether a trend exists in
amplitudes of stimulation pulses delivered by IMD 110 over a period
of time (1426). When processing circuitry identifies a trend ("YES"
branch of block 1426), processing circuitry determines, based on
accelerometer data, a current posture of patient 105 and records a
current time of day during the period of time in which the trend
occurs (1428). The trend may represent a trend of stimulation
amplitudes that induces a desired sensation in patient 105 while
the patient is assuming the posture. Processing circuitry may
determine whether the trend has occurred more than a threshold
number of times over a period of time (1430). If the trend has
occurred more than the threshold number of times ("YES" branch of
block 1430), processing circuitry may determine whether the trend
is correlated with a posture of patient 105 (1432). If processing
circuitry determines that the trend is correlated with posture
("YES" branch of block 1432), processing circuitry may add a new
state to a control policy of IMD 110 (1434) which updates one or
more stimulation parameters when the trend is detected. If
processing circuitry determines that the trend is not correlated
with posture ("NO" branch of block 1432), processing circuitry may
add a new state to a control policy of IMD 110 (1436) which updates
one or more stimulation parameters at the time of day in which the
trend was detected.
[0192] FIG. 15 is a flow diagram illustrating an example operation
for generating a recommendation for controlling one or more therapy
parameters, in accordance with one or more techniques of this
disclosure. For convenience, FIG. 15 is described with respect to
IMD 110, and external programmer 150 of FIG. 1, IMD 200 of FIG. 2,
and external programmer 300 of FIG. 3. However, the techniques of
FIG. 15 may be performed by different components of IMD 110,
external programmer 150, IMD 200, and external programmer 300, or
by additional or alternative medical devices.
[0193] Processing circuitry may execute an algorithm for
recommending changes to a control policy which determines one or
more parameters for electrical stimulation delivered by IMD 110.
For example, it may be beneficial to customize electrical
stimulation parameters on a patient-by-patient basis, since leads
130 may be implanted slightly differently in each patient. For
example, a distance between electrodes 232, 234 and target tissue
of patient 105 may be different than the distance between
electrodes and target tissue of another patient. Additionally,
leads 130 may migrate within patient 105 over a period of time,
thus changing the stimulation parameters required for patient 105
to experience a desired effect. Processing circuitry may execute
the algorithm in order to obtain information for determining one or
more parameter recommendations in order to prevent IMD 110 from
delivering transient overstimulation to patient 105.
[0194] Processing circuitry may output, for display by a user
interface (e.g., user interface 356 of FIG. 3), a message
requesting patient 105 to perform an action (1502). The message for
display by the user interface may be in the form of text, e.g.,
"COUGH ONCE," "PLEASE ARCH YOUR BACK," but this is not required.
The message may include symbols, such as symbols depicting the
action which patient 105 is prompted to perform. In some examples,
processing circuitry may output the message in response to
receiving an instruction to execute an algorithm. In some examples,
processing circuitry outputs the message without receiving a prompt
to output the message. Processing circuitry may receive a message
indicating that the action is complete, but this is not required.
In some examples, processing circuitry may proceed with the
algorithm without receiving indication that the action by patient
105 is complete.
[0195] Processing circuitry may output, for display by the user
interface, a set of requests (1504). Processing circuitry may
output the set of requests for display by user interface in a
sequence. That is, processing circuitry may output a first request
for display, followed by a second request for display, followed by
a third request for display, and so on. The set of requests may
represent requests for information, such as requests for
information as to an existence or a nature of one or more
sensations experienced by patient 105 which relate to the action
performed by patient 105. For example, the set of requests may
include one or more requests prompting the user to indicate whether
the action caused an undesirable attribute during the action and/or
after the action. The set of requests may also include one or more
requests prompting the user to indicate an identity (e.g., intense
sensation, increased location, pulsating sensation, tingling
sensation, pressure sensation, tapping sensation, vibration
sensation, or any combination thereof) of the undesirable
attribute.
[0196] In some examples, processing circuitry may output the one or
more requests prompting the user to indicate the identity of the
sensation as a menu of sensations for selection via the user
interface. In some examples, processing circuitry may output the
one or more requests prompting the user to indicate the identity of
the sensation as a sequence of requests. Each request of the
sequence of requests may include a prompt for patient 105 to
indicate whether a particular sensation occurred responsive to the
action.
[0197] Processing circuitry may receive, from the user interface, a
set of responses (1506). In some examples, the set of responses may
include a response corresponding to each request of the set of
requests, but this is not required. In some examples, the set of
responses might not include a response to one or more requests of
the set of requests. When a first request of the set of requests
includes a prompt for the user to indicate whether the action
caused an undesirable attribute during the action, a first response
of the set of responses may include either a "yes" response or a
"no" response indicating whether the action caused an undesirable
attribute. In some examples, processing circuitry may receive the
set of responses as a sequence of responses. For example, the set
of requests and the set of responses may be interleaved such that
processing circuitry receives a response to a respective request
before outputting a subsequent request of the sequence of requests.
Processing circuitry may determine, based on the set of responses,
one or more parameters which define electrical stimulation (1508)
delivered by IMD 110. Processing circuitry may determine the one or
parameters based on whether the set of requests indicate an
undesirable attribute, when an undesirable attribute occurs
relative to an action, an identity of an undesirable attribute, or
any combination thereof.
[0198] FIG. 16 is a flow diagram illustrating an example operation
for outputting one or more requests and receiving one or more
responses in order to adjust stimulation to a patient by IMD 110,
in accordance with one or more techniques of this disclosure. FIG.
16 is described with respect to IMD 110, and external programmer
150 of FIG. 1, IMD 200 of FIG. 2, and external programmer 300 of
FIG. 3. However, the techniques of FIG. 16 may be performed by
different components of IMD 110, external programmer 150, IMD 200,
and external programmer 300, or by additional or alternative
medical devices.
[0199] In some examples, the example operation of FIG. 16 includes
outputting one or more requests and receiving one or more responses
to these requests in order to determine one or more parameters for
delivering electrical stimulation to patient 105. Processing
circuitry may trigger IMD 110 to collect one or more baseline
measurements (1602). For example, before guiding patient 105 to
perform any actions, processing circuitry may trigger a recording
of baseline data in the neurostimulator and processing circuitry
may prompt patient 105 to rate various perceptual levels. The
baseline measurements may include, for example, accelerometer data,
temperature data, blood oxygenation data, ECAP data, heart rate,
blood pressure, tissue impedance, or any combination thereof.
Subsequently, IMD 110 may record baseline measurements (1604).
[0200] Processing circuitry may trigger IMD 110 to start continuous
measurements (1606). For example, before guiding patient 105 to
perform one or more actions, processing circuitry may trigger the
IMD 110 to start a continuous recording of parameters such as
stimulation amplitude, ECAP features, a current classification of a
feature (e.g., a stimulation feature and/or an ECAP feature),
current control policy state, or any combination thereof.
Subsequently, processing circuitry may output an instruction for
patient 105 to perform an action (1608). In some examples, block
1608 may be an example of block 1502 of FIG. 15. After outputting
the instruction, processing circuitry may trigger IMD 110 to stop
recording the continuous measurements (1610). In some examples,
processing circuitry may instruct IMD 110 to perform the continuous
measurements so that data corresponding to one or more patient
parameters during the performance of the action is accessible for
analysis. In some cases, processing circuitry may analyze ECAP data
during the performance of the action in order to determine one or
more stimulation parameter adjustments for avoiding transient
overstimulation.
[0201] Processing circuitry may output a request representing a
prompt to indicate whether an undesirable attribute of a sensation
occurred during a performance of the action (1612). If processing
circuitry receives a response indicating that an undesirable
attribute occurred during the action ("YES" branch of block 1612),
processing circuitry may determine whether to change the control
policy (1614) which determines electrical stimulation delivered by
IMD 110. Processing circuitry may determine whether to prompt
patient 105 to perform or a new action or prompt patient 105 to
perform the same action (1616). If processing circuitry receives a
response indicating that an undesirable attribute did not occur
during the action ("NO" branch of block 1612), processing circuitry
may output a prompt to indicate whether an undesirable attribute
occurred after a performance of the action (1618).
[0202] If processing circuitry receives a response indicating that
an undesirable attribute occurred after the action ("YES" branch of
block 1618), processing circuitry may determine whether to change a
control policy (1620) which determines electrical stimulation
delivered by IMD 110 and subsequently the example operation
proceeds to block 1616. If processing circuitry receives a response
indicating that an undesirable attribute did not occur after the
action ("NO" branch of block 1618), the example operation proceeds
to block 1616.
[0203] FIGS. 17A-17B are flow diagrams illustrating an example
operation for outputting one or more requests and receiving one or
more responses, in accordance with one or more techniques of this
disclosure. FIGS. 17A-17B are described with respect to IMD 110,
and external programmer 150 of FIG. 1, IMD 200 of FIG. 2, and
external programmer 300 of FIG. 3. However, the techniques of FIGS.
17A-17B may be performed by different components of IMD 110,
external programmer 150, IMD 200, and external programmer 300, or
by additional or alternative medical devices.
[0204] In some examples, processing circuitry outputs an
instruction for display by a user interface of a patient programmer
(e.g., user interface 356 of external programmer 300), the
instruction representing a prompt for patient 105 to perform an
action. After patient 105 completes the action, external programmer
300 may "interview" patient 105 to gather information on specific
attributes of one or more sensations felt by patient 105 during or
close to a period of time in which patient 105 performs the action.
In some examples, processing circuitry may use a current setting of
the control policy combined with patient perceptual input to
determine a recommended change in a control policy of IMD 110. The
recommended change may be implemented automatically by processing
circuitry, in some cases, or by a user (e.g., patient 105 or a
clinician) in other cases. After the recommended change is
implemented, processing circuitry may determine whether to output
an instruction for patient 105 to repeat the action in order to
perform a follow-up assessment to interview patient 105 again. It
may be beneficial for processing circuitry to store patient
responses over a period of time in order to employ smarter,
improved methods of changing stimulation parameters and store
information concerning other stimulation and lead properties (e.g.,
lead migration) as compared with techniques in which patient
responses are not stored.
[0205] Processing circuitry may receive an indication to execute an
interrogation program (1702). In some cases, the interrogation
program may be referred to herein as "Patient Guidance Wizard." In
some examples, the indication to execute the interrogation program
represents a user input to a device (e.g., an input to user
interface 356 of external programmer 300). In some examples, the
indication to execute the interrogation program represents an
automatic indication, such as a regular indication to execute the
interrogation program at a point in time. In some examples,
processing circuitry receives the indication in response to
external programmer 300 turning on. In some examples, processing
circuitry may receive the indication to execute the interrogation
program in response to the example operation of FIG. 14 arriving at
block 1412.
[0206] In order to start the interrogation program, processing
circuitry triggers one or more baseline measurements (1704). In
some examples, the one or more baseline measurements may include
biomarker measurements and system state measurements. For example,
the baseline measurements may include one or more of baseline ECAP
measurements, baseline heart rate measurements, baseline
respiratory rate measurements, baseline blood pressure
measurements, and other types of baseline biometric measurements.
The one or more baseline measurements may be useful for comparing
with one or more parameter measurements captured throughout the
interrogation program.
[0207] Additionally, processing circuitry may output one or more
prompts for information concerning baseline perception levels of
patient 105 and a baseline location of paresthesia sensation
(1706). In turn, processing circuitry may receive information
indicative of the baseline perception levels of patient 105 and the
baseline location. Baseline perception levels may represent one or
more sensations felt by patient 105 prior to performing any actions
related to the interrogation program and the baseline location may
represent the location of stimulation prior to performing any
actions related to the interrogation program. The one or more
prompts for information concerning baseline perception levels of
patient 105 may include a prompt for a current status of
paresthesia delivered by IMD 110. The prompt for the current status
of the paresthesia may include a request for a numerical rating on
a scale, such as a rating of the intensity of the stimulation from
1 to 10. In some examples, a "1" rating represents a faint tingling
sensation, a "5" rating represents a moderate prickly sensation,
and a "10 rating represents a heavy thumping sensation.
Additionally, or alternatively, the prompt for the current status
of the paresthesia may include a request for a baseline discomfort
level of patient 105 with "1" representing the least amount of
discomfort and "10" representing the greatest amount of discomfort.
The prompt for the baseline location may include a request for an
identification of a location (e.g., a location of the body) in
which patient 105 feels stimulation.
[0208] The processing circuitry triggers IMD 110 to start
collecting one or more continuous measurements (1708). As referred
to herein, a "continuous measurement" may represent a parameter
measurement which is recorded such that changes in the respective
parameter may be viewed over the period of time in which the
continuous measurement is taken. In other words, a continuous
measurement may represent a sequence of samples of the respective
parameter, where the sequence of samples is collected by IMD 110 at
a sampling rate. In some examples, the one or more continuous
measurements may include a continuous heart rate measurement, a
continuous blood pressure measurement, a continuous respiratory
measurement, a continuous accelerometer measurement, a continuous
ECAP measurement, or any combination thereof. The continuous ECAP
measurement may represent a continuous sense signal including one
or more ECAPS, where processing circuitry is configured to identify
the one or more ECAPS in the sense signal.
[0209] Processing circuitry outputs an instruction for patient 105
to perform an action (1710) for display by a user interface. The
action may include any one or more of a set of transient patient
actions such as a cough, a back arch, a Valsalva maneuver, a
leg-lift, or another kind of movement. Transient patient actions
may include any sort of movement that could possibly cause one or
more electrodes of leads 130 to move closer to or farther away from
target tissue of patient 105. As an example, responsive to
outputting the instruction, user interface 356 may display the
message "PLEASE COUGH ONCE," thus instructing the patient to cough
in order to perform a transient patient action which may briefly
change a distance between the one or more electrodes of leads 130
and target tissue of patient 105. In some examples, processing
circuitry may receive, from external programmer 300 or another
device, an indication that the action is complete. For example,
when the action is one cough, patient 105 may provide an input
indicating that the cough is complete to user interface 356, and
external programmer 300 may forward the patient input to processing
circuitry. Responsive to the action being complete, processing
circuitry triggers a stop of collecting one or more continuous
measurements (1712). In some examples, processing circuitry may
save the one or more continuous measurements to a memory for
analysis.
[0210] The interrogation program may include a set of requests
delivered in a sequence, and a set of responses, where the set of
requests at least partially depends on the set of responses. The
set of requests and the set of responses may be interleaved. For
example, processing circuitry may output a first request, receive a
first response to the first request, output a second request based
on the first response, receive a second response, and so on. As
such, the interrogation program may represent a logical flow which
may proceed based on the set of responses received by processing
circuitry.
[0211] Processing circuitry may output, for display by user
interface 356, a request to identify whether an undesirable
attribute occurred during a performance of the action (1714). For
example, processing circuitry may output a request which includes
the message "Was some attribute of the paresthesia undesirable
while performing the action? (Yes or No)." In this way, the request
to identify whether an undesirable attribute occurred during the
performance of the action may represent a first request of a set of
requests, the first request prompting the user to identify whether
the action caused an undesirable attribute (e.g., undesirable
sensation). Processing circuitry may receive, from external
programmer 300, a response to the request to identify whether the
undesirable attribute occurred during the performance of the action
(1716). Responsive to receiving a response which identifies that an
undesirable attribute occurred during the performance of the action
("YES" branch of block 1716), processing circuitry may output one
or more requests for an identification of an identity of the
undesirable attribute (1718). For example, processing circuitry may
output the message "Select the paresthesia attribute that was
undesirable DURING the action: too intense, pulsating feeling,
increased location, or none."
[0212] The one or more requests for the identification of the
identity of the undesirable attribute may include a request
corresponding to each undesirable attribute of a set of undesirable
attribute including but not limited, e.g., high intensity,
pulsating feeling, and increased or undesired location. Processing
circuitry outputs a request for an indication as to whether an
intensity of stimulation delivered by IMD 110 is uncomfortably high
during the performance of the action (1720). In response to
receiving a response that the intensity of the stimulation is not
uncomfortably high during the performance of the action ("NO"
branch of block 1720), processing circuitry outputs a request as to
whether the undesirable attribute represents an increased location
sensation (1722). In response to receiving a response that the
undesirable attribute is not an increased location sensation ("NO"
branch of block 1722), processing circuitry outputs a request as to
whether the undesirable attribute represents an undesirable
pulsating sensation (1724). In response to receiving a response
that the undesirable attribute is not a pulsating sensation ("NO"
branch of block 1722), processing circuitry may determine that the
undesirable attribute is none of an uncomfortably high intensity,
an increased location, or a pulsating sensation and the
interrogation operation proceeds to block 1726 where processing
circuitry sets an indication to request that patient 105 perform a
"next" action which is different from the action corresponding to
the current interrogation. It is not required for processing
circuitry to output three requests (blocks 1720, 1722, 1724) each
representing one of three sensations. Alternatively, in some cases,
processing circuitry may output a single request including a menu
of sensations for selection by patient 105.
[0213] In response to receiving a response that the intensity of
the stimulation is uncomfortably high during the performance of the
action ("YES" branch of block 1720), processing circuitry may
output one or more requests for an identification of whether the
uncomfortably high intensity occurs at a beginning of the action,
occurs at an end of the action, or occurs throughout an entire
period of time in which the action is performed (1728).
Additionally, in response to receiving a response that the
undesirable attribute is an increased location sensation ("YES"
branch of block 1722), processing circuitry may output one or more
requests for an identification of whether the uncomfortable
increased location sensation occurs at a beginning of the action,
occurs at an end of the action, or occurs throughout an entire
period of time in which the action is performed (1730). In this
way, processing circuitry may output a prompt for information as to
when the undesirable attribute occurs relative to the action in
both cases where the undesirable attribute represents an
uncomfortably high intensity and where the undesirable attribute
represents an uncomfortably increased location of stimulation.
[0214] Processing circuitry outputs a request for an identification
of whether the undesirable attribute occurs at the beginning of the
performance of the action (1732). Responsive to receiving a
response that the undesirable attribute does not occur at the
beginning of the performance of the action ("NO" branch of block
1732), processing circuitry outputs a request for an identification
of whether the undesirable attribute occurs at the end of the
performance of the action (1734). Responsive to receiving a
response that the undesirable attribute does not occur at the end
of the performance of the action ("NO" branch of block 1734),
processing circuitry determines that the undesirable attribute
occurs throughout the performance of the action and processing
circuitry outputs a request for an identification of whether an
overstimulation threshold of IMD 110 is currently higher than a
desirable overstimulation threshold value (1736).
[0215] It may be beneficial for processing circuitry to determine
whether the uncomfortable sensation occurs at the beginning of the
action, at the end of the action, consistently throughout the
performance of the action, or intermittently throughout the
performance of the action. As such, processing circuitry may
determine one or more control policy changes to be implemented such
that the same action, when performed again, will not cause the same
undesirable attribute felt by patient 105 during the interrogation
operation of FIGS. 17A-17B.
[0216] In response to receiving a response that the undesirable
attribute occurs at the beginning of the performance of the action
("YES" branch of block 1732), processing circuitry may generate a
recommendation to increase a decrement step size of one or more
stimulation pulses delivered by IMD 110 (1738). In response to
receiving a response that the undesirable attribute occurs at the
end of the performance of the action ("YES" branch of block 1734),
processing circuitry may generate a recommendation to decrease an
increment step size of one or more stimulation pulses delivered by
IMD 110 (1740). The action which processing circuitry prompts
patient 105 to perform may represent a transient patient action
which moves one or more electrodes of lead 130 closer to target
tissue of patient 105, causing IMD 110 to decrement an amplitude of
stimulation pulses delivered to the target tissue at a beginning of
the transient patient action and increment an amplitude of
stimulation pulses delivered to the target tissue at an end of the
transient patient action.
[0217] When processing circuitry receives an indication that an
uncomfortable sensation occurs at the beginning of the action, it
may be beneficial for processing circuitry to recommend increasing
the decrement step size of stimulation pulses delivered by IMD 110
such that, if the recommendation is implemented, stimulation pulses
are decreased at a greater rate of speed as compared with a time
prior to the recommendation by processing circuitry. Additionally,
when processing circuitry receives an indication that an
uncomfortable sensation occurs at the end of the action, it may be
beneficial for processing circuitry to recommend decreasing the
increment step size of stimulation pulses delivered by IMD 110 such
that, if the recommendation is implemented, stimulation pulses are
increased at a lesser rate of speed as compared with a time prior
to the recommendation by processing circuitry. Such recommendations
by processing circuitry, if implemented, may decrease a likelihood
that patient 105 experiences an uncomfortable stimulation (e.g.,
transient overstimulation) in the future while performing the same
action prompted by processing circuitry as a part of the
interrogation operation.
[0218] When processing circuitry receives an indication that the
overstimulation threshold is currently higher than a desirable
overstimulation threshold value ("YES" branch of block 1736),
processing circuitry may generate a recommendation to decrease the
overstimulation threshold. When processing circuitry receives an
indication that the overstimulation threshold is not currently
higher than a desirable overstimulation threshold value ("NO"
branch of block 1736), processing circuitry may generate a
recommendation to decrease a buffer zone lower boundary of one or
more stimulation pulses delivered by IMD 110 (1744). The buffer
zone may represent a range of ECAP amplitudes for which the IMD 110
holds stimulation element constant. As such, by decreasing the
buffer zone lower boundary, IMD 110 may decrease the threshold for
increasing stimulation amplitude.
[0219] When processing circuitry receives a response that the
undesirable attribute represents an undesirable pulsating sensation
("YES" branch of block 1724), processing circuitry may determine
whether an increment rate (e.g., increment step size) of one or
more stimulation pulses delivered by IMD 110 is greater than a
desirable increment rate value. When processing circuitry
determines that the increment rate is greater than the desirable
increment rate value ("YES" branch of block 1746), processing
circuitry may generate a recommendation to decrease the increment
rate (1748). When processing circuitry determines that the
increment rate is not greater than the desirable increment rate
value ("NO" branch of block 1746), processing circuitry may
generate a recommendation to increase a size of a hysteresis band
for more stimulation pulses delivered by IMD 110 (1750).
[0220] In response to generating the recommendation to increase the
decrement rate (e.g., decrement step size) of one or more
stimulation pulses delivered by IMD 110, generating the
recommendation to decrease the increment rate of one or more
stimulation pulses delivered by IMD 110, generating the
recommendation to decrease the overstimulation threshold,
generating a recommendation to increase a buffer zone size, or
generating the suggestion to decrease the buffer zone lower
boundary, processing circuitry may set an indication to prompt
patient 105 to repeat the same action (1752) as the action prompted
by processing circuitry during the present interrogation operation.
As such, the interrogation operation of FIGS. 17A-17B may be
repeated, causing processing circuitry to prompt patient 105 to
perform the same action over again and allowing processing
circuitry to evaluate the same action again.
[0221] When processing circuitry receives a response to request to
identify whether an undesirable attribute occurred during a
performance of the action indicating that an undesirable attribute
did not occur during the performance of the action ("NO" branch of
block 1716), processing circuitry may output a request for
information as to whether an undesirable attribute occurs after the
performance of the action (1754) and processing circuitry may
receive a response to the request (1756). When the response
indicates an undesirable attribute did not occur after the
performance of the action ("NO" branch of block 1756), processing
circuitry may determine whether to repeat the interrogation
operation. When the response indicates an undesirable attribute
does occur after the performance of the action ("YES" branch of
block 1756), processing circuitry may output, for display by the
user interface, a request for information as to an identity of the
undesirable attribute which occurs after the performance of the
action (1758). For example, processing circuitry may output the
message: "Select the paresthesia attribute that was undesirable
AFTER the action: too intense, temporary loss of paresthesia, none"
for display by the user interface. Processing circuitry may receive
a response that the stimulation intensity is uncomfortably high
(1760). In this case, processing circuitry generates a
recommendation to decrease a maximum stimulation amplitude (1764).
Processing circuitry may receive a response that the uncomfortable
sensation represents a temporary loss of paresthesia (1762). In
this case, processing circuitry generates a recommendation to
increase an increment step size of one or more stimulation pulses
generated by IMD 110 (1766).
[0222] If processing circuitry determines that the undesirable
attribute occurring after the sensation is neither related to high
intensity or temporary loss of paresthesia, the interrogation
operation may proceed to block 1726 and processing circuitry may
set an indication to perform the next action. In response to
generating the recommendations of blocks 1764 and 1766, processing
circuitry may set an indication to prompt patient 105 to repeat the
same action (1752) as the action prompted by processing circuitry
during the present interrogation operation. At block 1772,
processing circuitry may determine whether to restart the
interrogation operation by generating a request for patient 105 to
perform an action or end the process.
[0223] FIG. 18 is a flow diagram illustrating an example for saving
one or more sets of histogram data, in accordance with one or more
techniques of this disclosure. FIG. 18 is described with respect to
IMD 110 and external programmer 150 of FIG. 1, IMD 200 of FIG. 2,
and external programmer 300 of FIG. 3. However, the techniques of
FIG. 18 may be performed by different components of IMD 110,
external programmer 150, IMD 200, and external programmer 300, or
by additional or alternative medical devices.
[0224] When utilizing evoked compound action potentials (ECAPs) as
inputs to estimate a volume of tissue activation during the
delivery of electrical current to the nervous system (e.g., spinal
cord), a need exists to record attributes of the physiological
signal and delivery system which are then correlated to patient
105's perception of the therapy and/or therapy efficacy. If too
much tissue is activated, the patient may feel a sharp increase in
stimulation or perceived paresthesia from the stimulation delivered
by IMD 110 or similar unwanted side-effects. If too little tissue
is activated, the patient may experience a loss of therapeutic
benefit and a return of symptoms. A control policy executed by IMD
110 measures the tissue activation and adjusts stimulation based on
a volume of tissue activated.
[0225] During a configuration and adjustment of the control policy
executed by IMD 110, measurements of one or more characteristics
may be used to allow continued refinement of the control policy,
including characteristics such as a patient input of an intensity
of an undesirable attribute, various features of an ECAP at a time
of the undesirable attribute, a stimulation amplitude at a time of
the undesirable attribute, response times of the control policy at
the time of the undesirable attribute, and background symptom
levels. Data collection throughout the day is also needed even when
the patient is not perceiving unwanted side-effects. For example,
the control policy may be oversensitive to potential undesirable
attributes and therefore drive the delivered stimulation amplitude
down which in turn causes a return of symptoms and/or a loss of
paresthesia. In these cases, the system could be responding too
soon to measured biomarkers that are not accurately indicating a
potential undesirable attribute. This data shall be used to
evaluate how effective ECAP stimulation control is at improving
pain management and patient comfort. This needs to be evaluated
relative to optimization of the system parameters.
[0226] This disclosure describes one or more techniques for
addressing a need to collect the attributes introduced above with a
limited amount of memory located on IMD 110. For example, it might
not be possible to continuously collect histogram data over several
days or weeks and store the histogram data to a memory. As such,
IMD 110 may periodically collect histogram data for a period of
time, within the limits of the IMD 110 memory. The durations and
resolutions of histograms generated by IMD 110 may be
configurable.
[0227] IMD 110 may collect periodic sets of histogram data
continuously in the background for one or more of a set of
attributes. The set of attributes may include stimulation
amplitudes, ECAP feature amplitudes, an amount of time in each
control policy state, and motion signal amplitudes. In some
examples, each set of histogram data may correspond to a window of
time. In some examples, a duration of the window of time may be
within a range from 3 minutes to 10 minutes (e.g., 5 minutes), but
this is not required. The duration of the window of time of the
histogram may be greater than 10 minutes or less than 3 minutes, in
some examples. Since each patient's amplitude ranges for the
attributes are different, the histogram bin "dividers" are
configurable.
[0228] IMD 110 may also collect rolling buffer histogram data
(smaller time duration of each histogram results in higher temporal
resolution in overall recording). This histogram buffer is not
saved to recording memory until an external indication is received
from the patient indicating that an undesirable attribute was
experienced. The idea is that the 3-minute buffer will be long
enough in duration to capture the characteristics of the
undesirable attribute which occurred before the patient trigger.
When an undesirable attribute is experienced, the patient needs
time to retrieve the patient programmer, start the programmer, and
send the trigger.
[0229] Other external events may be correlated to the physiological
conditions, such as when the patient starts and stops an activity
(e.g. going for a walk, going to sleep) and when the patient
adjusts some parameter of the system (e.g., control policy
threshold). These events are recorded as time stamps which then can
be indexed into the periodic histograms during post processing.
[0230] In some examples, patient 105 may retrieve external
programmer 150 (1802) in response to experiencing an undesirable
attribute. External programmer 150 receives a user input indicating
an undesirable attribute (e.g., "zinger") (1804). Additionally, in
some cases, external programmer 150 may receive data indicative of
a cause of the undesirable attribute and an intensity of the
undesirable attribute. The external programmer 150 records the
intensity of the undesirable attribute and the cause of the
undesirable attribute in storage device 354 (1806).
[0231] In response to receiving the user input indicating the
undesirable attribute, external programmer 150 sends an event
trigger to IMD 110 (1808), where the event trigger indicates the
user identification of the undesirable attribute. IMD 110 may save
histogram data stored in a rolling buffer of IMD 110 (1810). For
example, the histogram data stored by the rolling buffer at a time
in which IMD 110 receives the event trigger may include histogram
data 1812. In order to permanently save histogram data 1812, IMD
110 may permanently save histogram data 1812 to a memory of IMD
110. The permanently stored histogram data may include histogram
data 1816.
[0232] IMD 110 may, in some cases, permanently store sets of
histogram data on a regular basis. For example, histogram data set
1818, histogram data set 1820, histogram data set 1850, histogram
data set 1852, and histogram data set 1854 may represent histogram
data sets which are stored by IMD 110 on a regular basis. In some
examples, IMD 110 may automatically store histogram data sets
according to a predetermined frequency (e.g., hourly, daily). These
automatically recorded histogram data sets may each correspond to a
window of time having a predetermined length (e.g., 5 minutes).
[0233] In some examples, IMD 110 may also permanently save
information (e.g., an event type and a timestamp) corresponding to
an event indicated by patient 105. For example, external programmer
150 may receive user input indicating a start of an event (1822).
Additionally, external programmer 150 may also receive information
indicative of a description of the event. External programmer 150
records the information indicative of the description of the event
in a memory (1824). External programmer 150 sends a message
indicating a first timestamp marking the start of the event to IMD
110 (1826). IMD 110 saves the first timestamp marking the start of
the event and saves a type of the event (1828). The information
including the first timestamp and the type is saved to the memory
of IMD 110 as information 1830. External programmer 150 may receive
user input indicating an end of an event (1832). External
programmer 150 sends a message indicating a second timestamp
marking the end of the event to IMD 110 (1834). IMD 110 saves the
second timestamp marking the end of the event (1836). Second
timestamp 1838 marks the end of the event in the memory of IMD
110.
[0234] The first timestamp and the second timestamp may be applied
during an analysis of histogram data automatically captured by IMD
110. For example, processing circuitry may identify first histogram
data that is collected by IMD 110 closest to the time of the first
timestamp and processing circuitry may identify second histogram
data that is collected by IMD 110 closest to the time of the second
timestamp. Processing circuitry may, in some cases, identify one or
more additional sets of histogram data which occur between the
first set of histogram data and the second set of histogram data
(e.g., during the event). The first histogram data may indicate one
or more conditions at the start of the event and the second
histogram data may indicate one or more conditions at the end of
the event. Processing circuitry may analyze the first histogram
data and the second histogram data in order to determine whether
any of the one or more conditions have changed from the start of
the event to the end of the event. Based on this analysis,
processing circuitry may determine whether to recommend one or more
alterations to the control policy of IMD 110. Additionally, the
description of the event may be applied during the analysis of the
histogram data automatically captured by IMD 110. Histogram data
collected by IMD 110 during or close in time to the event may be
analyzed as being associated with the event, so that processing
circuitry may identify one or more trends associated with the
event.
[0235] Processing circuitry may record one or more timestamps
corresponding to parameter changes initiated by external programmer
150. For each instance that external programmer 150 initiates a
change of one or more parameters which define stimulation delivered
by IMD 110, processing circuitry may record a timestamp
corresponding to the parameter change. For example, external
programmer 150 may receive a user selection of a new parameter
(1840). External programmer 150 initiates a change to the new
parameter (1842) and record a timestamp corresponding to the change
to the new parameter (1846). The timestamp may be saved to a memory
of the IMD 110 and/or a memory of the external programmer 150 as
information 1848.
[0236] The timestamp indicating the parameter change may be applied
during an analysis of histogram data automatically captured by IMD
110. For example, histogram data 1852 is collected by IMD 110 close
to a time of the timestamp indicating the parameter change (e.g.,
information 1848). Additionally, histogram data 1850 is collected
by IMD 110 before the timestamp indicating the parameter change and
histogram data 1854 is collected by IMD 110 before the timestamp
indicating the parameter change. As such, processing circuitry may
analyze histogram data 1850, histogram data 1852, and histogram
data 1854 in order to determine an effect of the parameter change
on one or more aspects (e.g., a size of one or more bins) of the
histogram data. In some examples, based on this analysis,
processing circuitry may generate a recommendation to change the
control policy of IMD 110. In some examples, based on this
analysis, processing circuitry may generate a recommendation to
maintain the control policy of IMD 110 at a current state.
[0237] FIG. 19 is a graph 1900 illustrating ECAP amplitudes of a
set of ECAPs sensed by IMD 110 over an 11 second period of time
associated with a transient overstimulation event, in accordance
with one or more techniques of this disclosure. In some examples,
IMD 110 records the ECAPs at 50 Hz. As seen in graph 1900, ECAP
amplitudes are greatest during seconds 6-8 of the plot. This
increase in ECAP amplitudes may represent an uncomfortable
attribute of a sensation experienced by the patient. As seen in
FIG. 19, each one-second window of graph 1900 includes a set of
data points, where each data point represents an amplitude of an
ECAP measured by IMD 110 at the time corresponding to the position
of the respective data point on the x-axis of graph 1900.
Amplitudes of measured ECAPs vary within respective 1-second
windows, and this variance may be seen in histogram data
corresponding to the data points shown in graph 1900.
[0238] FIG. 20 is a graph 2000 which illustrates histogram data
including a set of histograms corresponding to the data of graph
1900 in FIG. 19, in accordance with one or more techniques of this
disclosure. As seen FIG. 20, graph 2000 includes a set of
histograms 2010-2030. Although the set of histograms shown in graph
2000 includes 11 histograms (e.g., one histogram for each one
second period of time of the total 11 second event), a set of
histogram data representing 11 seconds may include more than 11
histograms or less than 11 histograms. For example, histogram data
may include 3 minutes of one-second histograms, that is, 180
one-second histograms, in other examples. However, each "bin" of
time for a respective histogram may be shorter or longer than 1
second in other examples. As seen in the example of FIG. 20,
histograms 2020, 2022, and 2024 indicate that seconds 6-8 include
more high-amplitude ECAPs than other histograms such as histogram
2010. This may indicate that patient 105 experiences transient
overstimulation at seconds 6-8 and the magnitude of those sensed
ECAPs.
[0239] The following examples are example systems, devices, and
methods described herein.
[0240] Example 1: A system includes: a user interface; and
processing circuitry configured to: output, for display by the user
interface, a message requesting the patient perform a set of
actions; receive, from the user interface, user input indicative of
a patient response associated with the set of actions; and
determine, based on the user input, one or more adjustments to a
control policy which controls electrical stimulation delivered by a
medical device based on at least one evoked compound action
potentials (ECAP) sensed by the medical device.
[0241] Example 2: The system of example 1, where the system further
includes: communication circuitry configured to communicate with
the medical device, where the processing circuitry is configured to
output, to the medical device via the communication circuitry, an
instruction to configure the one or more adjustments to the control
policy.
[0242] Example 3: The system of any of examples 1-2, where the
electrical stimulation includes a plurality of informed pulses and
a plurality of control pulses, each control pulse of the plurality
of control pulses eliciting a respective ECAP of the plurality of
ECAPs, where the control policy controls, based on the plurality of
ECAPs, one or more parameters corresponding to the plurality of
control pulses delivered by the medical device, and where the
control policy controls, based on the plurality of ECAPs, one or
more parameters corresponding to the plurality of informed pulses
delivered by the medical device.
[0243] Example 4: The system of any of examples 1-3, where the
control policy controls one or more parameters of the electrical
stimulation therapy delivered by the medical device, where the
electrical stimulation therapy includes a plurality of stimulation
pulses, and where to determine the one or more adjustments to the
control policy, the processing circuitry is configured to:
determine the one or more adjustments in order to cause the control
policy to perform any one or combination of decrease a decrement
step size or a decrement step rate of the plurality of stimulation
pulses responsive to one or more events associated with the patient
response, increase the decrement step size or the decrement step
rate of the plurality of stimulation pulses responsive to the one
or more events associated with the patient response, decrease an
increment step size or an increment step rate of the plurality of
stimulation pulses responsive to the one or more events associated
with the patient response, and increase the increment step size or
the increment step rate of the plurality of stimulation pulses
responsive to the transient one or more events associated with the
patient response.
[0244] Example 5: The system of any of examples 1-4, where the
processing circuitry is further configured to: output, for display
by the user interface, a set of requests, where each request of the
set of requests includes a prompt for information relating to one
or more patient sensations corresponding to the action, and where
to receive the user input indicative of the patient response, the
processing circuitry is configured to: receive, from the user
interface, a set of responses, where each response of the set of
responses represents a patient response to a respective request of
the set of requests.
[0245] Example 6: The system of any of examples 1-5, where the
processing circuitry is configured to: output, for display by the
user interface, a first request of the set of requests, where the
first request includes a prompt for the user to indicate whether
the set of actions caused an undesirable sensation during the set
of actions; and receive, from the user interface, a first response
of the set of responses, where the first response includes a
patient response that the set of actions caused an undesirable
sensation during the set of actions or a patient response that the
set of actions did not cause an undesirable sensation during the
set of actions.
[0246] Example 7: The system of any of examples 1-6, where
responsive to receiving the patient response that the set of
actions caused an undesirable sensation during the set of actions,
the processing circuitry is configured to: output, for display by
the user interface, a group of second requests of the set of
requests, where the group of second requests include a prompt for
the user to identify the undesirable sensation from a menu of
possible undesirable sensations; receive, from the user interface,
a group of second responses of the set of responses, where the
group of second responses include a user identification of the
undesirable sensation from the menu of undesirable sensations; and
determine, based on the group of second responses, the one or more
adjustments to the control policy.
[0247] Example 8: The system of any of examples 1-7, where
responsive to receiving the patient response that the set of
actions did not cause an undesirable sensation during the set of
actions, the processing circuitry is configured to: output, for
display by the user interface, a second request of the set of
requests, where the second request includes a prompt for the user
to indicate whether the set of actions caused an undesirable
sensation after the set of actions; and receive, from the user
interface, a second response of the set of responses, where the
second response includes a patient response that the set of actions
caused an undesirable sensation after the set of actions or a
patient response that the set of actions did not cause an
undesirable sensation after the set of actions.
[0248] Example 9: The system of any of examples 1-8, where
responsive to receiving the patient response that the set of
actions caused an undesirable sensation after the set of actions,
the processing circuitry is configured to: output, for display by
the user interface, a group of third requests of the set of
requests, where the group of third requests include a prompt for
the user to identify the undesirable sensation from a menu of
possible undesirable sensations; receive, from the user interface,
a group of third responses of the set of responses, where the group
of third responses include a user identification of the undesirable
sensation from the menu of undesirable sensations; and determine,
based on the group of third responses, the one or more adjustments
to the control policy.
[0249] Example 10: The system of any of examples 1-9, where the set
of actions is a first set of actions, where the message is a first
message, and where responsive to receiving the patient response
that the first set of actions did not cause an undesirable
sensation after the first set of actions, the processing circuitry
is configured to: determine whether to prompt the patient to
perform a second set of actions; and responsive to determining to
prompt the patient to perform a second set of actions, output a
second message for display by the user interface, the second
message requesting the patient to perform the second set of
actions.
[0250] Example 11: The system of any of examples 1-10, where the
processing circuitry is further configured to: output, prior to
outputting the message requesting the patient to perform the set of
actions, an instruction for the medical device to measure one or
more parameters; and receive, from the medical device, data
indicative of the one or more measured parameters, where the data
corresponds to a period of time including the set of actions
performed by the patient.
[0251] Example 12: The system of any of examples 1-11, where the
one or more parameters include any one or combination of a
stimulation amplitude of one or more stimulation pulses of the
electrical stimulation therapy, characteristics of evoked compound
action potentials (ECAPs) responsive to the one or more stimulation
pulses, an electrogram (EGM) of the patient, a motion level of the
patient, or any combination thereof.
[0252] Example 13: The system of any of examples 1-12, where the
medical device includes an implantable medical device (IMD).
[0253] Example 14: The system of any of examples 1-13, where an
external device includes the user interface.
[0254] Example 15: A method including: outputting, by processing
circuitry for display by the user interface, a message requesting
the patient perform a set of actions; receiving, by the processing
circuitry from the user interface, user input indicative of a
patient response associated with the set of actions; and
determining, by the processing circuitry based on the user input,
one or more adjustments to a control policy which controls
electrical stimulation delivered by a medical device based on at
least one evoked compound action potentials (ECAP) sensed by the
medical device.
[0255] Example 16: The method of example 15, further including
outputting, by the processing circuitry to the medical device via
communication circuitry, an instruction to configure the one or
more adjustments to the control policy.
[0256] Example 17: The method of any of examples 15-16, where the
control policy controls one or more parameters of the electrical
stimulation therapy delivered by the medical device, where the
electrical stimulation therapy includes a plurality of stimulation
pulses, and where to determining the one or more adjustments to the
control policy includes: determining the one or more adjustments in
order to cause the control policy to perform any one or combination
of decrease a decrement step size or a decrement step rate of the
plurality of stimulation pulses responsive to one or more events
associated with the patient response, increase the decrement step
size or the decrement step rate of the plurality of stimulation
pulses responsive to the one or more events associated with the
patient response, decrease an increment step size or an increment
step rate of the plurality of stimulation pulses responsive to the
one or more events associated with the patient response, and
increase the increment step size or the increment step rate of the
plurality of stimulation pulses responsive to the transient one or
more events associated with the patient response.
[0257] Example 18: The method of any of examples 15-17, where the
method further includes: outputting, by processing circuitry for
display by the user interface, a set of requests, where each
request of the set of requests includes a prompt for information
relating to one or more patient sensations corresponding to the
action, and where to receiving the user input indicative of the
patient response includes: receiving, from the user interface, a
set of responses, where each response of the set of responses
represents a patient response to a respective request of the set of
requests.
[0258] Example 19: The method of any of examples 15-18, where the
method further includes: outputting, by processing circuitry for
display by the user interface, a first request of the set of
requests, where the first request includes a prompt for the user to
indicate whether the set of actions caused an undesirable sensation
during the set of actions; and receiving, by processing circuitry
from the user interface, a first response of the set of responses,
where the first response includes a patient response that the set
of actions caused an undesirable sensation during the set of
actions or a patient response that the set of actions did not cause
an undesirable sensation during the set of actions.
[0259] Example 20: The method of any of examples 15-19, where
responsive to receiving the patient response that the set of
actions caused an undesirable sensation during the set of actions,
the method further includes: outputting, by the processing
circuitry for display by the user interface, a group of second
requests of the set of requests, where the group of second requests
include a prompt for the user to identify the undesirable sensation
from a menu of possible undesirable sensations; receiving, by the
processing circuitry from the user interface, a group of second
responses of the set of responses, where the group of second
responses include a user identification of the undesirable
sensation from the menu of undesirable sensations; and determining,
by the processing circuitry based on the group of second responses,
the one or more adjustments to the control policy.
[0260] Example 21: The method of any of examples 15-20, where
responsive to receiving the patient response that the set of
actions did not cause an undesirable sensation during the set of
actions, the method further includes: outputting, by the processing
circuitry for display by the user interface, a second request of
the set of requests, where the second request includes a prompt for
the user to indicate whether the set of actions caused an
undesirable sensation after the set of actions; and receiving, by
the processing circuitry from the user interface, a second response
of the set of responses, where the second response includes a
patient response that the set of actions caused an undesirable
sensation after the set of actions or a patient response that the
set of actions did not cause an undesirable sensation after the set
of actions.
[0261] Example 22: The method of any of examples 15-21, where
responsive to receiving the patient response that the set of
actions caused an undesirable sensation after the set of actions,
the method further includes: outputting, by the processing
circuitry for display by the user interface, a group of third
requests of the set of requests, where the group of third requests
include a prompt for the user to identify the undesirable sensation
from a menu of possible undesirable sensations; receiving, by the
processing circuitry from the user interface, a group of third
responses of the set of responses, where the group of third
responses include a user identification of the undesirable
sensation from the menu of undesirable sensations; and determining,
by the processing circuitry based on the group of third responses,
the one or more adjustments to the control policy.
[0262] Example 23: The method of any of examples 15-22, where the
set of actions is a first set of actions, where the message is a
first message, and where responsive to receiving the patient
response that the first set of actions did not cause an undesirable
sensation after the first set of actions, the method further
includes: determining, by the processing circuitry, whether to
prompt the patient to perform a second set of actions; and
responsive to determining to prompt the patient to perform a second
set of actions, outputting, by the processing circuitry, a second
message for display by the user interface, the second message
requesting the patient to perform the second set of actions.
[0263] Example 24: The method of any of examples 15-23, further
including: outputting, by the processing circuitry prior to
outputting the message requesting the patient to perform the set of
actions, an instruction for the medical device to measure one or
more parameters; and receiving, by the processing circuitry from
the medical device, data indicative of the one or more measured
parameters, where the data corresponds to a period of time
including the set of actions performed by the patient.
[0264] Example 25: A computer-readable medium including
instructions that, when executed by a processor, causes the
processor to: output, for display by the user interface, a message
requesting the patient perform a set of actions; receive, from the
user interface, user input indicative of a patient response
associated with the set of actions; and determine, based on the
user input, one or more adjustments to a control policy which
controls electrical stimulation delivered by a medical device based
on at least one evoked compound action potentials (ECAP) sensed by
the medical device.
[0265] Example 26: A medical device including: stimulation
generation circuitry configured to deliver electrical stimulation
to a patient, where the electrical stimulation therapy includes a
plurality of stimulation pulses; sensing circuitry configured to
sense one or more evoked compound action potentials (ECAPs), where
the sensing circuitry is configured to sense each ECAP of the one
or more ECAPs elicited by a respective stimulation pulse of the
plurality of stimulation pulses; and processing circuitry
configured to store a set of histogram data corresponding to a set
of ECAPs of the plurality of ECAPs, the set of ECAPs being sensed
by the sensing circuitry over a window of time.
[0266] Example 27: The medical device of example 26, where the set
of histogram data includes a set of histogram bins, where each
histogram bin of the set of histogram bins corresponds to a range
of ECAP parameter values, and where each histogram bin of the set
of histogram bins includes a number of ECAPs of the set of ECAPs
that are associated with a parameter value within the respective
range of ECAP parameter values.
[0267] Example 28: The medical device of any of examples 26-27,
where the processing circuitry is further configured to: receive
information indicative of a patient response; and capture, in
response to receiving the user input indicative of the patient
response, the set of histogram data in a memory, where the set of
histogram data includes data representative of the patient
response.
[0268] Example 29: The medical device of any of examples 26-28,
where to store the set of histogram data, the processing circuitry
is configured to temporarily store the set of histogram data in a
rolling buffer which updates as time progresses.
[0269] Example 30: The medical device of any of examples 26-29,
where the processing circuitry is configured to: capture the set of
histogram data stored in the rolling buffer at a time in which the
processing circuitry receives the user input indicative of the
patient response, where the window of time extends from a first
time to a second time representing the time in which the processing
circuitry receives the user input or a time after the processing
circuitry receives the user input, and where the window of time
includes a period of time in which the patient response occurs.
[0270] Example 31: The medical device of any of examples 26-30,
where the processing circuitry is configured to: capture the set of
histogram data stored in the rolling buffer at a time following the
time in which the processing circuitry receives the user input
indicative of the patient response, where the window of time
extends from a first time to a second time representing the time in
following the time in which the processing circuitry receives the
user input, and where the window of time includes a period of time
in which the patient response occurs.
[0271] Example 32: The medical device of any of examples 26-31,
where the processing circuitry is configured to: receive a user
request to set one or more histogram parameters for collecting the
set of histogram data; and set, based on the user request, the one
or more histogram parameters, where the one or more histogram
parameters include a set of parameter ranges which define one or
more histogram bins included in a set of histogram bins of the
histogram data.
[0272] Example 33: The medical device of any of examples 26-32,
where the set of histogram data includes: a first histogram
corresponding to stimulation pulse amplitude values of a set of
stimulation pulses delivered by the stimulation generation
circuitry; and a second histogram corresponding to ECAP amplitude
values of ECAPs sensed by the sensing circuitry responsive to the
set of stimulation pulses delivered by stimulation generation
circuitry.
[0273] Example 34: The medical device of any of examples 26-33,
where the window of time is a first window of time, where the set
of histogram data includes a first set of histogram data, and where
the processing circuitry is further configured to: store a
plurality of second sets of histogram data, where each second set
of histogram data of the plurality of the second sets of histogram
data correspond to one or more ECAPs being sensed by the sensing
circuitry over a second window of time of a plurality of second
windows of time; and capture each second set of histogram data of
the plurality of second sets of histogram data to a memory.
[0274] Example 35: The medical device of any of examples 26-34,
where the processing circuitry is configured to: receive a user
report of a start of a patient activity; save a first timestamp
corresponding to the start of the patient activity; receive a user
report of an end of a patient activity; and save a second timestamp
corresponding to the end of the patient activity, where the first
timestamp corresponds to one of the plurality of second sets of
histogram data and the second timestamp corresponds to one of the
plurality of second sets of histogram data.
[0275] Example 36: A method including: delivering, by stimulation
generation circuitry, electrical stimulation to a patient, where
the electrical stimulation therapy includes a plurality of
stimulation pulses; sensing, by sensing circuitry, one or more
evoked compound action potentials (ECAPs), where the sensing
circuitry is configured to sense each ECAP of the one or more ECAPs
elicited by a respective stimulation pulse of the plurality of
stimulation pulses; and storing, by processing circuitry, a set of
histogram data corresponding to a set of ECAPs of the plurality of
ECAPs, the set of ECAPs being sensed by the sensing circuitry over
a window of time.
[0276] Example 37: The method of example 36, where the set of
histogram data includes a set of histogram bins, where each
histogram bin of the set of histogram bins corresponds to a range
of ECAP parameter values, and where each histogram bin of the set
of histogram bins includes a number of ECAPs of the set of ECAPs
that are associated with a parameter value within the respective
range of ECAP parameter values.
[0277] Example 38: The method of any of examples 36-37, where the
method further includes: receiving, by the processing circuitry,
information indicative of a patient response; and capturing, by the
processing circuitry in response to receiving the user input
indicative of the patient response, the set of histogram data in a
memory, where the set of histogram data includes data
representative of the patient response.
[0278] Example 39: The method of any of examples 36-38, where
storing the set of histogram data includes temporarily storing the
set of histogram data in a rolling buffer which updates as time
progresses.
[0279] Example 40: The method of any of examples 36-39, where the
method further includes: capturing, by the processing circuitry,
the set of histogram data stored in the rolling buffer at a time in
which the processing circuitry receives the user input indicative
of the patient response, where the window of time extends from a
first time to a second time representing the time in which the
processing circuitry receives the user input or a time after the
processing circuitry receives the user input, and where the window
of time includes a period of time in which the patient response
occurs.
[0280] Example 41: The method of any of examples 36-40, where the
method further includes: capturing, by the processing circuitry,
the set of histogram data stored in the rolling buffer at a time
following the time in which the processing circuitry receives the
user input indicative of the patient response, where the window of
time extends from a first time to a second time representing the
time in following the time in which the processing circuitry
receives the user input, and where the window of time includes a
period of time in which the patient response occurs.
[0281] Example 42: The method of any of examples 36-41, where the
method further includes: receiving, by the processing circuitry, a
user request to set one or more histogram parameters for collecting
the set of histogram data; and setting, by the processing circuitry
based on the user request, the one or more histogram parameters,
where the one or more histogram parameters include a set of
parameter ranges which define one or more histogram bins included
in a set of histogram bins of the histogram data.
[0282] Example 43: The method of any of examples 36-42, where the
window of time is a first window of time, where the set of
histogram data includes a first set of histogram data, and where
the method further includes: storing, by the processing circuitry,
a plurality of second sets of histogram data, where each second set
of histogram data of the plurality of the second sets of histogram
data correspond to one or more ECAPs being sensed by the sensing
circuitry over a second window of time of a plurality of second
windows of time; and capturing, by the processing circuitry, each
second set of histogram data of the plurality of second sets of
histogram data to a memory.
[0283] Example 44: The method of any of examples 36-43, where the
method further including: receiving, by the processing circuitry, a
user report of a start of a patient activity; saving, by the
processing circuitry a first timestamp corresponding to the start
of the patient activity; receiving, by the processing circuitry, a
user report of an end of a patient activity; and saving, by the
processing circuitry, a second timestamp corresponding to the end
of the patient activity, where the first timestamp corresponds to
one of the plurality of second sets of histogram data and the
second timestamp corresponds to one of the plurality of second sets
of histogram data.
[0284] Example 45: A computer-readable medium including
instructions that, when executed by a processor, causes the
processor to: deliver electrical stimulation to a patient, where
the electrical stimulation therapy includes a plurality of
stimulation pulses; sense one or more evoked compound action
potentials (ECAPs), where the sensing circuitry is configured to
sense each ECAP of the one or more ECAPs elicited by a respective
stimulation pulse of the plurality of stimulation pulses; and store
a set of histogram data corresponding to a set of ECAPs of the
plurality of ECAPs, the set of ECAPs being sensed by the sensing
circuitry over a window of time.
[0285] The techniques described in this disclosure may be
implemented, at least in part, in hardware, software, firmware, or
any combination thereof. For example, various aspects of the
techniques may be implemented within one or more microprocessors,
DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete
logic QRS circuitry, as well as any combinations of such
components, embodied in external devices, such as physician or
patient programmers, stimulators, or other devices. The terms
"processor" and "processing circuitry" may generally refer to any
of the foregoing logic circuitry, alone or in combination with
other logic circuitry, or any other equivalent circuitry, and alone
or in combination with other digital or analog circuitry.
[0286] For aspects implemented in software, at least some of the
functionality ascribed to the systems and devices described in this
disclosure may be embodied as instructions on a computer-readable
storage medium such as RAM, DRAM, SRAM, FRAM, magnetic discs,
optical discs, flash memory, or forms of EPROM or EEPROM. The
instructions may be executed to support one or more aspects of the
functionality described in this disclosure.
[0287] In addition, in some aspects, the functionality described
herein may be provided within dedicated hardware and/or software
modules. Depiction of different features as modules or units is
intended to highlight different functional aspects and does not
necessarily imply that such modules or units must be realized by
separate hardware or software components. Rather, functionality
associated with one or more modules or units may be performed by
separate hardware or software components or integrated within
common or separate hardware or software components. Also, the
techniques could be fully implemented in one or more circuits or
logic elements. The techniques of this disclosure may be
implemented in a wide variety of devices or apparatuses, including
an IMD, an external programmer, a combination of an IMD and
external programmer, an integrated circuit (IC) or a set of ICs,
and/or discrete electrical circuitry, residing in an IMD and/or
external programmer.
* * * * *